There is a unanimous consensus among the classical scholars of Islam that there is no particular age limit when marriage can occur between 2 parties. Since there is no minimum age, Muslim men can marry females of any age, even babies in the cradle. But there is a condition when it comes to intercourse: the wife must be able to handle it. If a prepubescent wife is not able to handle intercourse, it is forbidden to perform the act until she reaches the age of 9, at which point, the husband may go in as he pleases. But the husband may also go in even before the age of 9 if she is able to handle it. If she cannot, intercourse is forbidden but the husband may perform other sexual acts to gratify himself.
Here is IslamQA:
Marrying a young girl before she reaches the age of adolescence is permitted in sharee’ah; indeed it was narrated that there was scholarly consensus on this point.
(a)Allah says (interpretation of the meaning):
“And those of your women as have passed the age of monthly courses, for them the ‘Iddah (prescribed period), if you have doubt (about their periods), is three months; and for those who have no courses [(i.e. they are still immature) their ‘Iddah (prescribed period) is three months likewise”
[al-Talaaq 65:4]
In this verse we see that Allah has made the ‘iddah in the case of divorce of a girl who does not have periods – because she is young and has not yet reached puberty – three months. This clearly indicates that Allah has made this a valid marriage.
(b)It was narrated from ‘Aa’ishah (may Allah be pleased with her) that the Prophet (peace and blessings of Allah be upon him) married her when she was six years old, he consummated the marriage with her when she was nine and she stayed with him for nine years.
(Narrated by al-Bukhaari, 4840; Muslim, 1422)
The Prophet (peace and blessings of Allah be upon him) married ‘Aa’ishah when she was six years old and consummated the marriage when she was nine.”
(Narrated by al-Bukhaari and Muslim; Muslim says ‘seven years’)
The fact that it is permissible to marry a young girl does not mean that it is permissible to have intercourse with her; rather that should not be done until she is able for it. For that reason the Prophet (peace and blessings of Allah be upon him) delayed the consummation of his marriage to ‘Aa’ishah. Al-Nawawi said: With regard to the wedding-party of a young married girl at the time of consummating the marriage, if the husband and the guardian of the girl agree upon something that will not cause harm to the young girl, then that may be done. If they disagree, then Ahmad and Abu ‘Ubayd say that once a girl reaches the age of nine then the marriage may be consummated even without her consent, but that does not apply in the case of who is younger. Maalik, al-Shaafa’i and Abu Haneefah said: the marriage may be consummated when the girl is able for intercourse, which varies from one girl to another, so no age limit can be set. This is the correct view. There is nothing in the hadeeth of ‘Aa’ishah to set an age limit, or to forbid that in the case of a girl who is able for it before the age of nine, or to allow it in the case of a girl who is not able for it and has reached the age of nine. Al-Dawoodi said: ‘Aa’ishah (may Allah be pleased with her) was reached physical maturity (at the time when her marriage was consummated).
Sharh Muslim, 9/206
It is preferable for a guardian not to marry off his daughter when she is still young unless there is a valid reason for that.
Al-Nawawi said:
It should be noted that al-Shaafa’i and his companions said: It is preferable for fathers and grandfathers not to marry off a virgin until she reaches the age of puberty and they ask her permission, lest she end up in a marriage that she dislikes. What they said does not go against the hadeeth of ‘Aa’ishah, because what they meant is that they should not marry her off before she reaches puberty if there is no obvious interest to be served that they fear will be missed out on if they delay it, as in the hadeeth of ‘Aa’ishah. In that case it is preferable to go ahead with the marriage because the father is enjoined to take care of his child’s interests and not to let a good opportunity slip away.
And Allah knows best.
Sharh Muslim, 9/206.
(IslamQA – On acting; and the ruling on marrying young girls, Question 22442)
Here also are the scholars:
“Muslim schools of jurisprudence UNANIMOUSLY allow the marriage of young girls, even if they were still babies in the cradle. But intercourse cannot occur until the girl can withstand penetration.”
(Ibn Hajar al-Asqalani, Fath al-Bari, Volume 11, p. 25)
The famous commentator on Sahih Muslim, an-Nawawi, says that when a minor is ready:
“for sex, it is permissible at any time given there is no harm to the girl and both the husband and the girls’ guardian approve. According to Ahmad (ibn Hanbal) if they don’t agree, she is forced to join her husband at 9 years”
(Sharh Muslim, volume 3, p. 577)
In cases where intercourse is forbidden, such as when the wife is on her menses (Q2:222) or when she is too young to handle it, one may perform what is known as “thighing”. Here is what thighing is:
The term Mufaakhathah means to have foreplay with the wife in between her thighs. It is reported in one narration that when the Prophet wanted to enjoy one of his wives who was in menstruation, he would put a piece of cloth on her vagina (i.e. cover it). [Ibn Maajah].
The author of Faydh Al-Qadeer interpreted the expression ‘if he wanted to enjoy to mean having all permissible foreplay but avoiding the vagina [or the anus], like in between her thighs (i.e. Mufaakhathah).
Allaah Knows best.
(IslamWeb)
Here is the reference it mentions:
It was narrated from Mu’awiyah bin Abu Sufyan that:
He asked Umm Habibah, the wife of the Prophet: “What did you used to do with the Messenger of Allah when you were menstruating?” She said: “If it was at the beginning of the period when the bleeding is heavy, we would tie the waist-wrapper tightly around our thighs, then lie down with the Messenger of Allah.”