The Prophet’s, sallallaahu ‘alayhi wa sallam, marriage to `Aa'ishah, may Allaah be pleased with her
18-6-2002 | IslamWeb
Question:
I have a question about the marriage of 'Aa'ishah, may Allaah be pleased with her, to the Prophet, sallallaahu 'alayhi wa sallam. What was her exact age when she married the Prophet, sallallaahu 'alayhi wa sallam? Was she only 9-12 years old when she married the Prophet, sallallaahu 'alayhi wa sallam who was around 50 years old? Can a man have sexual intercourse with so small a girl at this age? Did the Prophet, sallallaahu 'alayhi wa sallam, wait until she reached puberty? Were there some signs that 'Aa'ishah, may Allaah be pleased with her, was at the age of puberty when she married the Prophet, sallallaahu 'alayhi wa sallam (such as increase in height, development of breasts and hair in the pubic area and under arms)? Al-Muhallab said, "[The scholars] Agreed that it is permissible for a father to marry off his young virgin daughter, even though it is not usually the case to have intercourse with such a young woman." Is it true that Sheikh al-Muhallab said this? When did 'Aa'ishah, have her first intercourse with the Prophet, sallallaahu 'alayhi wa sallam, and when did she get her menstrual period?
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
The Prophet 
only held his marriage contract with `Aa'ishah 
when she was six years old, but he consummated the marriage when she was nine years old, as reported by Al-Bukhari and others 
.
This fact is reported in many books of Seerah (biography) through many chains of narrators that cannot be rejected.
In fact, the Prophet did not take consummate the marriage till she reached the age of puberty and was able to bear having sexual intercourse. For that reason, she used to say, "When a girl reaches the age of nine, she becomes a woman." [Ahmad and At-Tirmithi] Imaam Ash-Shaafi'i 
said, “I saw a grandmother who was only twenty-one years old.” This means that she and her daughter as well became pregnant before the age of ten years.
Therefore, a man may marry a small girl but he can only establish conjugal relations with her after she becomes pubescent. Ibn Hajar reported that marrying a small girl is permissible but having sexual intercourse is only permissible after her puberty.
What is reported from Muhallab is conforming to the opinion of other scholars as reported by Ash-Shawkaani who said, “All Muslim scholars agree that a father can marry off his minor girl.” This means he can merely conduct the marriage contract, but it does not mean permitting her husband to have conjugal relations with her since she would be unable to bear that.
Allaah Knows best.