You may have noticed that both critics of Islam and a handful of Muslims eager to paint themselves as the antitheses of the West have often attempted to demonstrate that child marriage is sanctioned in the Quran, directly or indirectly, by referring to verse 65:4 to support their claim.
In this post, I will present my understanding of the verse (the understanding taken by most Muslims, and those defending Islam), as well as analysing some common apologetics used against this understanding - in this case, through the lens of my discussions with a user of this subreddit, u/justrollinyaknow (hereafter referred to as "JR"), and his posts and comments on the topic. There will be a focus on his post "What is the meaning of نساء in verse 65:5 of the Quran?", which is based around many of the common arguments used here by critics of Islam.
Please note that when referencing the Holy Quran, I have used non-Ahmadi verse numbering throughout, since that is what most people are familiar with and search for. JR has used the Ahmadi numbering system (which includes bismillah, adding one to the verse number), so if you don't find a verse where it's meant to be, check the ones immediately before and after.
I have also added transliterations in addition to Arabic text where possible to accommodate those who may not be able to read Arabic. These transliterations can be easily verified by referring to a word-by-word Quran, or by listening to a recitation of the relevant verse online.
When quoting other people, I have left the quote untouched - any errors are from the original material.

Contents

• 1. Background to this post
• 2. 65:4 explained
• 2.1. Evidence - the use of nisaa
• 2.2. Evidence - the grammar of the Arabic verbs
• 2.3. Evidence - age of marriage in the Quran
• 3. Criticism of this understanding - an analysis of u/justrollinyaknow's post
• 4. Conclusion
• 5. Sources and further reading

1. Background to this post

Quite a while back, u/justrollinyaknow and I had a discussion on verse 65:4 here on the islam_ahmadiyya subreddit. This initial conversation was relatively short; he chose to break off the discussion, and we parted ways amicably.
A short time later, JR decided to write up a more detailed post on the topic, and I in turn left a brief response in the comments section (if you follow the link, you can see the full conversation - parts of which are quoted below - underneath that comment).
However, he was unhappy with my reply:

You are grasping at straws, just so as to win by the skin of your teeth.

Somewhat surprised at his statement, I requested that he write a reply to my critique instead of insulting me. In response, he said:

I have nothing to critique. You have not critiqued anything...aside for being partial and believing your Jama'at's position is the correct one and speaking with confidence.

(Of course, I would receive a rather large amount of criticism if I used these tropes in response to criticisms of Islam :) but I digress.)
Eventually, JR stated that he would not engage with responses of the type I had provided, and requested that I write up a more detailed post explaining my viewpoint on the verse if I wanted him to engage. I agreed to write a more expanded response. JR replied:

Take your time; take as much time as you need. Give me your best work.
I'll be waiting at the finish line with a red marker. Oh shiz, better buy me pack of 12. This is gonna be bloody.

After requesting one last time that he reply to my original comment on his post - a request that he refused - we parted ways again, agreeing to pick up the discussion again when my more detailed post was complete. This, of course, is that post. It is obviously intended as a follow-up to the specific points raised by JR, but its main purpose is as a general informational article about this issue.

2. 65:4 explained

The verse itself is as follows:

وَ الّٰٓیِٴۡ یَئِسۡنَ مِنَ الۡمَحِیۡضِ مِنۡ نِّسَآئِکُمۡ اِنِ ارۡتَبۡتُمۡ فَعِدَّتُہُنَّ ثَلٰثَۃُ اَشۡہُرٍ ۙ وَّ الّٰٓیِٴۡ لَمۡ یَحِضۡنَ ؕ وَ اُولَاتُ الۡاَحۡمَالِ اَجَلُہُنَّ اَنۡ یَّضَعۡنَ حَمۡلَہُنَّ ؕ و مَنۡ یَّتَّقِ اللّٰہَ یَجۡعَلۡ لَّہٗ مِنۡ اَمۡرِہٖ یُسۡرًا -
Wa-allāi ya-is'na mina l-maḥīḍi min nisāikum ini ir'tabtum fa'iddatuhunna thalāthatu ashhurin wa-allāī lam yaḥiḍ'na. Wa-ulātu l-aḥmāli ajaluhunna an yaḍaʿna ḥamlahunna. Waman yattaqi l-laha yajʿal lahu min amrihi yus'ran.
"And if you are in doubt as to such of your women as despair of monthly courses, then know that the prescribed period for them is three months, and the same is for such as have not had their monthly courses yet. And as for those who are with child, their period shall be until they are delivered of their burden. And whoso fears Allah, He will provide facilities for him in his affair." (65:5)

[N.B - I have used exactly the same translation JR does in his post.]
The meaning of this verse is relatively straightforward. It is describing how to deal with divorced women - specifically, it sets out their waiting periods after divorce (a procedure with two main purposes: to give the two a chance to consider their decision and re-initiate the marriage if desired, and to ensure that if a child is born after the divorce, the parents can be identified). The verse describes three special cases:

1. Those women who "despair of monthly courses"

This part of the verse refers to those women who, for whatever reason, have ceased to menstruate after having done so normally previously. It refers to women who have reached menopause, but also refers to women who have stopped menstruating for other reasons, like secondary amenorrhea - that is, women who have ceased to menstruate but should still be doing so. This may be due to various reasons, including illness, medical/hormonal disorders, stress, irregular eating, low body weight, low body fat percentage, or heavy exercise and athletic activity (something that can happen even through recreational practice).

1. Those women who are pregnant.

No detailed exegesis required here. Pregnant women are instructed that their waiting period will be as long as they remain pregnant; it will last until they have given birth.

1. Those who "have not menstruated".

I save this for last because this, of course, is the main area of contention.
This section of the verse refers to those females who have not menstruated yet, but are otherwise mature. The most common explanation for this is a condition called primary amenorrhea. This is when menstruation is delayed, or does not occur, despite being otherwise physically mature (but it may still occur). Primary amenorrhea can occur for similar reasons to secondary amenorrhea - it is often due to genetic conditions and medical problems, but obviously can occur as a result of disordered eating, exercise, or a low body fat percentage (physical activity and low body fat percentages are a common cause of amenorrhea) at the time when menstruation is expected to begin.
It appears to me that given the environment and lifestyle of seventh century Arabia, this "athletic amenorrhea" may well have not been unusual. It can also be pointed out that historically, menstruation used to occur later, often after a female was otherwise mature (perhaps due to this very reason), but, in any case, I will stick to the amenorrhea explanation for now. Expanding on these points is currently beyond the scope of this post.
It is also possible to make the case for this being a scientific miracle of the Quran, as it can be argued that prophet Muhammad (saw) could not have known about a condition only identified by medical practitioners centuries later - a valid argument. However, that is an entirely different discussion, and I will leave this open for the reader to ponder over. I personally think that there are better verses to use for this purpose, but those wanting to investigate further are welcome to do so.
Returning to the understanding I have presented, there are three main points to consider here which support this point of view.
2.1. Evidence - the meaning of nisaa
Marriage in Islam is fundamentally an institution to both physically and emotionally fulfill the natural desires and needs of an individual which develop as he/she matures, as well as an institution to produce children. Because of this, marriage is intended to be a contract between two mature people.
The Quran, when referring to marriage and conjugal relationships, always uses the word nisaa, meaning "women". This can be verified in any dictionary, but you can refer here) to the Quranic Arabic Corpus for now. (Note that they have translated nisaa in 4:127 as "girls". JR has used this as an argument as well. Be sure to remember this - we will be returning to this point in section 3 to demonstrate why this understanding is erroneous).
Some verses demonstrating this use of nisaa:

"It is not allowed to thee to marry women (nisaa) after that..." (33:52)
"And marry not those women (nisaa) whom your fathers had married..." (4:22)
"And the divorced women (nisaa) shall wait concerning themselves for three courses; and it is not lawful for them that they conceal what Allah has created in their wombs, if they believe in Allah and the Last Day..." (2:228)

The word unthaa (females in general) is not used here. If the Quran sanctioned marriage with prepubescent girls, one would expect unthaa (females in general) to have been used, so as not to limit marriage to nisaa as the Quran does.
Expanding further, nisaa means females who are physically mature - i.e, women who have developed secondary sexual characteristics - and, furthermore, females who are mentally mature, in that they are capable of managing their own affairs and the responsibilities of a marriage (see section 2.3). What is key to note, though, is that the word certainly does not refer to prepubescent girls. Interestingly, if you look at words for "girl" in Arabic, nisaa is conspicuously absent. Food for thought? Perhaps.
Some objections to this definition will be covered in my analysis of JR's post in Section 3.
2.2. Evidence - the grammar of the Arabic verbs
Now we need to go back to the Arabic and take a closer look at the words of the verse. The exact words are وَّ الّٰٓیِٴۡ لَمۡ یَحِضۡنَ, or wa-allāī lam yaḥiḍ'na ("and those [women] who have not menstruated").
The bit we are interested in is lam yaḥiḍ'na ("have not menstruated") - this is basically the central argument of this allegation, after all. There are three components to this phrase:

1. Lam - the negative participle ("not").
2. Ya and na - these conjugate the verb to the feminine plural third person imperfect.
3. Yaḥiḍ'na - the actual imperfect verb ("menstruate").

The actual imperfect verb itself, though, does not refer to a specific tense. The tense is determined by the negative participle lam (used for the past tense). This verb is also in the jussive mood, denoting hope or expectation.
What does all this mean, though? If you don't have experience with languages, you might be wondering what the point of all this analysis is. Some, though, will have already realised what I'm getting at.
Simply put, lam denotes negation explicitly in the past tense - something that did not happen. The jussive mood implies expectation. A more accurate translation, then, would be "those who did not menstruate as expected, but still hope to do so". (Of course, this translation is somewhat cumbersome, but I personally think that conveying the full meaning is important enough to warrant some sacrifice of flow).
What does that sound like to you? Negation in the past tense, but still with an aspect of expectation or hope... it seems to fit quite well into point 3 of section 2, doesn't it - primary amenorrhea and all that?
Now, if you want to edit your copy of the Quran to make this verse refer to prepubescent girls who haven't menstruated yet - easy. Just change the lam to lan to show negation in the future tense ("those who have not yet menstruated at all and are hoping to do so").
Note the difference. Now, there's no aspect of past negation - it's been replaced with a purely future-centred negation.
2.3. Evidence - age of marriage in the Quran
To supplement the case for this understanding of the verse, we can also go elsewhere in the Quran to see if there is any reference to the age of marriage. One verse often used for this purpose is 4:6 -

"And test the orphans [in their abilities] until they reach marriageable age. Then if you perceive in them sound judgement, release their property to them..." (4:6)

Marriageable age here is associated with sound judgement, and fully developed abilities (both mental and physical). This would seem to imply at least some standard of maturity - a standard of maturity high enough to warrant entrusting property to them.
Since this is only a supplementary point, and JR previously objected at my referencing verses other than 65:4 to make my point (despite his post relying heavily on other verses of the Quran) -

Stick to verse 65:5. Period.

- I will not go into too much detail on this particular line of argument. Such discussions are beyond the scope of this particular article anyway, which will focus on exploring 65:4. This article provides a good explanation of 4:6 and other verses referring to marriageable age in the Quran. I highly recommend you have a read and then return to this post, as I will be referring to 4:6 in the next section, where we will be analysing other pertinent verses of the Quran. It will, of course, be of benefit to you if you familiarise yourself with this particular verse beforehand.

3. Criticism of this understanding - an analysis of u/justrollinyaknow's post

Now we'll take a look at the objections raised by JR in his post. Before you read my thoughts, be sure to follow this link to read his original post in full (as well as our exchange in the comments below).
https://www.reddit.com/islam_ahmadiyya/comments/cphrgb/what_is_the_meaning_of_%D9%86%D8%B3%D8%A7%D8%A1_in_verse_655_of_the/
(This section was originally based loosely off my original comment in response to his post, but I have had to make quite a few additions and expansions.)
The main area of contention, as JR points out, is the meaning of nisaa. If we want to establish who the part of the verse in question (females who have not menstruated) refers to, we need to establish what it means. (This is, of course, ignoring the fact that the very tense of the verbs in the verse does not allow for JR's interpretation, whether nisaa refers to newborn babies, pensioners, Daleks, or anything else. For the sake of argument, I will overlook this inconvenient point for now). Words, after all, can take different meanings based on context, but if you want to translate a word in a different way to its standard meaning, you need to provide evidence for the alternative understanding. Thus, he suggests two possible alternative translations for the word nisaa, which he says are taken from the Quran itself: "wife" and "girl".
We begin with the first meaning, "wife". JR correctly points to 2:187 of the Quran, where "women" is used as a stand-in for "wife" - and at first, it appears to be a valid point. A similar feature of using the word for “women” as a word for “wife” exists in other languages too (e.g. Spanish). However, that fact made me realise that the word still carries the connotations of maturity evident when it means “woman”. That is, as far as I know, it would be odd to call a married eight-year-old a nisaa. The specific word “wife” could be used, yes, but “nisaa” would carry the wrong connotations. The word nisaa refers to physical maturity. Of course, one could also point out that the word still means "woman" - it is just understood to mean "wife", as that's the easiest way to translate it into English.
While we’re on the topic, though, I’ll point out why I think JR's wider point here is illogical anyway. A large part of his argument is centred around the idea that

even if a child, a prepubescent girl, who is married, she would be considered a woman. A girl who is not a virgin is considered a woman, she is not referred to as a girl anymore.

But consider whether you would call an eight-year old girl who has had sex a “woman”. Does an eight-year old girl become a woman if she loses her virginity? If marriage/virginity is a deciding factor in this definition, would the argument hold true for a girl even younger than that? What about if a baby has a marriage arrangement signed?
Obviously not. We are not concerned here with who is married and who is a virgin. We are concerned with maturity.
A second, supplementary point can be raised here in light of the actual topic of the chapter - divorce. We've gotten so caught up in the possible meanings of nisaa that we've overlooked the obvious: there are no "wives" anywhere in this verse. After all, it deals with women who have actually been divorced, rather than dealing with married couples. 2:231 of the Quran appears to support this (And when you divorce women and they have [nearly] fulfilled their term), putting "divorce" before the completion of the waiting period, but it is obviously a rather obvious connection to make anyway. The meaning of "wife", then, cannot really apply. These are, in essence, "ex-wives".
​
We now turn our attention to the second meaning, which is the crux of JR's argument. Here, JR uses 4:127 to try and show that nisaa means "girl". Unfortunately, this is simply incorrect. This is, in fact, a classic case of making the Arabic fit the English. Since this is a more significant point than the previous one - and it also led me down an interesting rabbit hole of translations - we will spend a little more time trying to understand why it is misleading. Here is the passage we are concerned with:

وَ یَسۡتَفۡتُوۡنَکَ فِی النِّسَآءِ ؕ قُلِ اللّٰہُ یُفۡتِیۡکُمۡ فِیۡہِنَّ ۙ وَ مَا یُتۡلٰی عَلَیۡکُمۡ فِی الۡکِتٰبِ فِیۡ یَتٰمَی النِّسَآءِ الّٰتِیۡ لَاتُؤۡ تُوۡنَہُنَّ مَا کُتِبَ لَہُنَّ وَ تَرۡغَبُوۡنَ اَنۡ تَنۡکِحُوۡہُنَّ وَ الۡمُسۡتَضۡعَفِیۡنَ مِنَ الۡوِلۡدَانِ ۙ وَ اَنۡ تَقُوۡمُوۡا لِلۡیَتٰمٰی بِالۡقِسۡطِ ؕ وَ مَا تَفۡعَلُوۡا مِنۡ خَیۡرٍ فَاِنَّ اللّٰہَ کَانَ بِہٖ عَلِیۡمًا (۴:۱۲۸)
"And they seek of thee the decision of the Law with regard to women. Say, Allah gives you His decision regarding them. And so does that which is recited to you in the Book concerning the orphan girls whom you give not what is prescribed for them and whom you desire to marry, and concerning the weak among children. And He enjoins you to observe equity towards the orphans. And whatever good you do, surely Allah knows it well." (4:127)

This verse, interestingly enough, has been translated in quite a few different ways. I will address this point a little later, as it has a very significant implication - but first off, let's take a look at JR's point as he has presented it, on his terms, using this translation only.
Right off the bat, it’s obvious that nisaa is actually used both in the start of the verse as "women", and next to “orphans” as "girls" (see the bolded words in the Arabic, and their corresponding bolded word in the translation. Note how the first nisaa is made to correspond to "women", and the second nisaa to "girls".) What does this mean for us?
Well, JR's logic would probably work if the Arabic for “girl” was specifically used with “orphans”, because that would prove that immature girls also fall under the category of “nisaa” - but that’s not what the text says. What does the text do? It uses "women" (nisaa) twice. No girls anywhere in the verse.
In that case, why are we having this discussion in the first place? Where does this allegation come from? This is where my above comment about this verse having multiple translations comes in. I decided to cross-examine the verse's translation using a detailed word-by-word approach, because I had noticed a small inconsistency with the declension of nisaa and the subsequent translation of "orphan girls". Upon investigating a little further, it became apparent that the situation was rather more complicated than merely a small translation slip.
Before we go on, let's see the translations listed for this verse:

Sahih International: And they request from you, [O Muhammad], a [legal] ruling concerning women. Say, "Allah gives you a ruling about them and [about] what has been recited to you in the Book concerning the orphan girls to whom you do not give what is decreed for them - and [yet] you desire to marry them - and concerning the oppressed among children and that you maintain for orphans [their rights] in justice." And whatever you do of good - indeed, Allah is ever Knowing of it.
Pickthall: They consult thee concerning women. Say: Allah giveth you decree concerning them, and the Scripture which hath been recited unto you (giveth decree), concerning female orphans and those unto whom ye give not that which is ordained for them though ye desire to marry them, and (concerning) the weak among children, and that ye should deal justly with orphans. Whatever good ye do, lo! Allah is ever Aware of it.
Yusuf Ali: They ask thy instruction concerning the women. Say: Allah doth instruct you about them: And (remember) what hath been rehearsed unto you in the Book, concerning the orphans of women to whom ye give not the portions prescribed, and yet whom ye desire to marry, as also concerning the children who are weak and oppressed: that ye stand firm for justice to orphans. There is not a good deed which ye do, but Allah is well-acquainted therewith.
Shakir: And they ask you a decision about women say: Allah makes known to you His decision concerning them, and that which is recited to you in the Book concerning female orphans whom you do not give what is appointed for them while you desire to marry them, and concerning the weak among children, and that you should deal towards orphans with equity; and whatever good you do, Allah surely knows it.
Muhammad Sarwar: (Muhammad), they ask you concerning women. Tell them, "God will instruct you about them, besides that which can be read in the Book, about widows with children, whom you wanted to marry without giving them their due rights and He will instruct you about the rights of the weak and oppressed children. God commands you to maintain justice with the orphans. God knows all about whatever good you do.
Mohsin Khan: They ask your legal instruction concerning women, say: Allah instructs you about them, and about what is recited unto you in the Book concerning the orphan girls whom you give not the prescribed portions (as regards Mahr and inheritance) and yet whom you desire to marry, and (concerning) the children who are weak and oppressed, and that you stand firm for justice to orphans. And whatever good you do, Allah is Ever All­ Aware of it.
Arberry: They will ask thee for a pronouncement concerning women. Say: 'God pronounces to you concerning them, and what is recited to you in the Book concerning the orphan women to whom you give not what is prescribed for them, and yet desire to marry them, and the oppressed children, and that you secure justice for orphans. Whatever good you do, God knows of it.'

Now let's break down what the issues are here.
Firstly, it's worth returning briefly to our previous discussion of the use of nisaa in this verse to mean "girls". Only two of these seven translations have actually used this meaning, and in fact, Arberry has specifically used "women". These other translations have actually avoided using “girls”; indeed, it would appear that “nisaa” is used here specifically in the Arabic in order to emphasise that the females being discussed are physically mature. (N.B - someone may ask why "orphan" would be needed to describe a mature female. I would reply that it is to do with the lack of a guardian.)
To top it all off, not far from this verse, we actually see an instruction regarding the age of marriage - ironically, with reference to orphans. 4:6 reads:

And test the orphans [in their abilities] until they reach marriageable age. Then if you perceive in them sound judgement, release their property to them.

(See Section 2.3, and go here for a more detailed analysis.)
In light of this, it is very difficult to argue that marriage to prepubescent girls - and orphan girls, at that - is permissible.
What's happened here is that JR has seen a translation that uses “girls”, ignored the other translations, and tried to fit nisaa to that particular translation rather than actually translating the Arabic word itself. It’s worth pointing out that if you look for Arabic words that mean “girls”, nisaa is nowhere to be seen... food for thought.
My actual stance, though, is that the entire above discussion was a waste of time. Why?
Well, what's more interesting is how two other translations here have dispensed with the idea of marrying orphan girls/women/females completely, and have instead used "widows with children" (Muhammad Sarwar) and "orphans of women" (Yusuf Ali). Now, I mentioned earlier that the reason I started to dig a little deeper on this verse was because of an inconsistency I spotted in the declension of nisaa, and I will now elaborate on this point.
You see, in the Arabic, nisaa is in the genitive case, as l-nisāi, and the genitive case denotes posession (e.g, "the man's car", or "the car of the man"). When I looked at the translation in JR's post, though, no such idea was present. It had only been translated as "orphan girls".
Upon referring to the word-by-word translation, it became clear that such an idea was indeed present in the Arabic text.
The feminine plural \"nisaa\", seen here declined to give the genitive case.
Nisaa, then, is not an a noun being qualified by "orphan" here. It is in the genitive case, and thus we have to translate this part of the verse as "the orphans of the nisaa [to whom you do not give their dues, and yet desire to marry]".
However, we still need to determine who this "whom" is talking about. If it refers to the orphans, there is still room to salvage our critics' argument. However, it cannot refer to the orphans, because the relative pronoun allātī is feminine plural, agreeing with and thus referring to the feminine plural nisaa. "Orphans" (yataama) is masculine.
Now that we know this, we can very easily determine which of JR's proposed meanings of nisaa is applicable here: "girls" is rather implausible, since we're talking about females with children; "wives" is also unlikely, since we are talking about females that we can marry. "Women", then, is the only logical translation that works here.
Why this verse is mistranslated is beyond me. It is possible that it arises because of a desire to intentionally misrepresent the verse in order to support radical interpretations of Islam, or perhaps out of a desire to reconcile the verse and references to Aisha (ra)'s young age in the Hadith (which is another topic altogether). I prefer to be optimistic and say that it is just a consequence of mild carelessness, and simply "going with the flow" after seeing other (incorrect) translations - which seems to be a more plausible explanation than the aforementioned theories.
In any case, regardless of which of these two translations you want to use, the point still stands: nisaa in 4:127 does not refer to prepubescent females.

4. Conclusion

Now that we've analysed the verse in more detail, I hope that my position has become a little clearer. 65:4 does not allow marriage with prepubescent girls, because "women" - physically mature females - are the ones addressed in the verse. Attempts to prove otherwise fail because the alternative translations proposed are not suitable given the context, and/or are fundamentally incorrect. Furthermore, if we look closer at the grammar of the verse, it becomes clear that the females addressed are those who did not menstruate normally as they expected, but still may do so in the future (i.e those suffering from primary amenorrhea) - not those who have not menstruated at all and have never previously expected menstruation. Indeed, marriage in Islam is a serious contract designed to accommodate the needs of human beings that arise when they mature, and thus is a contract between two mature people; sound judgement, mental maturity, and physical maturity are required for two people to live together as husband and wife.

5. Sources and further reading

JR's post https://www.reddit.com/islam_ahmadiyya/comments/cphrgb/what_is_the_meaning_of_%D9%86%D8%B3%D8%A7%D8%A1_in_verse_655_of_the/
What causes amenorrhea? https://www.nichd.nih.gov/health/topics/amenorrhea/conditioninfo/causes
"Athletic amenorrhea" https://www.betterhealth.vic.gov.au/health/ConditionsAndTreatments/menstruation-athletic-amenorrhoea
The grammar of 65:4 http://quransmessage.com/articles/verse%2065-4%20FM3.htm
Marriageable age in the Quran http://quransmessage.com/articles/ayesha%20age%20FM3.htm
How should we translate 4:127? (scroll down to "Can One Marry Underage Orphans?") https://www.justislam.co.uk/errors-english-translations-the-quran-p-198.html
An analysis of various verses relating to the issue of child marriage https://www.islamahmadiyyamovement.com/post/age-of-marriage
The 65:4 child marriage claim refuted https://discover-the-truth.com/2016/03/12/quran-654-the-child-marriage-claim/