The Qur'an states that men may marry up to four women if they can deal justly with each woman (4:3); however, 33:50 exempts the Prophet (pbuh) - and only the Prophet - from this limitation:
"O Prophet! We have made lawful to thee thy wives to whom thou hast paid their dowers; and those whom thy right hand possesses out of the prisoners of war whom Allah has assigned to thee; and daughters of thy paternal uncles and aunts, and daughters of thy maternal uncles and aunts, who migrated (from Makkah) with thee; and any believing woman who dedicates her soul to the Prophet if the Prophet wishes to wed her;- this only for thee, and not for the Believers (at large); We know what We have appointed for them as to their wives and the captives whom their right hands possess;- in order that there should be no difficulty for thee. And Allah is Oft- Forgiving, Most Merciful." (33:50)
"Why is it acceptable that a prophet lusted after a girl at only 5, married her at only 6, and consummated the marriage at 9?"
The following was posted by a woman, "Ruqaiyyah," on Beliefnet back in April 2001. (I have taken the liberty of editing for spelling, punctuation and grammar; otherwise, this is as she wrote.) IMHO, this is one of the better answers to this type of question regarding Aishah.
"But let us start at the beginning with the facts; yes, the Prophet (pbuh) was over 50 when he was engaged to Aishah, who was perhaps only 6 years old, their physical marriage commencing three years later when she was 9. My first comment is to let you know that the scholars do actually differ in the information given; all the hadiths claiming that she was only 6 are based on Urwah, and are not from Madinah, which to many Sunni scholars makes them suspect. That is not to say they are not true, but they are 'suspected.' Secondly, you need to know that the birth and death dates of many of the Prophet's (pbuh) companions, including his wives, are not known for certain, and there are several possible dates given for many of them. Most scholars accept that Aishah died at the age of 67, but they give the date of 672 CE/ 50 AH, after a widowhood of 40 years. Just to give you an idea of the complication of it all, I would like to tell you in detail that there are three main theories –
"(1) The most widely accepted in the Muslim world, that Aishah was born in the 4th year of Prophethood, ie.614 CE, based on Ibn Sa'd's work. If true, she was 5 when Khadijah died, 6 at nikah, 9 at marriage, but these sources also suggest she was only 18 when Prophet died; this means she would only have been 58 in 672.
"(2) If she were born 4 years before the Prophethood, she would have been 14/15 when Khadijah died, 15/16 at nikah, 19 at year of marriage, 27/28 when he died, and would indeed have been 67/68 in 672.
"(3) Other hadiths say she was born five years after Fatimah, who was said to have been born 5 years before Prophethood, making Aishah's birth that year - 610. Then she would have been 9 when Khadijah died, 10 at nikah, 14 at marriage, 22 when he died, and 62 when she died. However, Fatimah's dates are also disputed.
"My own conclusion is that she was born in 605-6, and that Ibn Sa'd was cursed by a glaring example of writer's slip that went unnoticed by those who used him as their primary source. The slip, I believe, was that he stated Aishah was born in the 4th year of the Prophethood, when what he actually meant was 4 years before it. So, my first part of my answer is that the whole business of Aishah's age is debatable.
"The second part of my answer is to consider the thorny issue of pedophilia. There is all the difference in the world by adult men committing indecent sexual acts on small children, and the issue of love (which might not even be a physical thing at all) between an adult and a child. The Prophet (pbuh) was well known for his great love for children, but certainly with no sexual content to it whatsoever. He had many children himself, the four girls surviving and two sons dying, at which he adopted his four-year old cousin Ali and brought him up and also adopted a 14-year-old slave-boy, Zayd, and brought him up too. In later life, when he married his other wives, they also brought with him all their children by their previous marriages - for example, Umm Salamah came with 3 (and one born just after their marriage); Sawdah came with 6, etc. There was never any suggestion of pedophilia.
"At the same time, we have to realize that the culture was very different; the usual age for a girl's marriage was once she reached puberty and her periods commenced, thus making her technically 'adult'; it was the same for Jewish people - and we might observe how the Virgin Mary was presumably only 12 years old when she gave birth to Jesus, if the material about her upbringing and family background has any truth in it. Boys tended to marry for the first time round about the age of 15-16. In reality, many little girls of twelve or so have already experienced 'being in love', and boys tend to do so just a little later. It seems to be natural. Whether or not they should be having a sexual relationship at that age has varied in public opinion throughout the ages; in practice, many seem to do so, whether or not their families know about it. Certainly this seems to be the case in the UK. You are probably aware of the Muslim point of view that once a youngster shows signs of sexual urges that are becoming difficult to control, it is more sensible and kinder to get them married, (then they can have as much as they like, honorably), than let them risk all the consequences of sex outside marriage.
"Another aspect I would like you to consider is the very deep love that can exist between an older person and a tiny child. I cannot be the only grandma to whom a little grandson has seriously declared that he loves me, and will marry me when he grows up. I love him, too, more than any other human being. But you will have to take my word when I say there is no question of any pedophilia involved. You will also have to take my word when I tell you that when I was 12 I was deeply in love with our 45-year-old postmaster, at whose office I had a part-time job. I adored him - but again, no pedophilia whatsoever! And at that time, I also had plenty of toys to play with.
"So, I have to conclude that the love between the Prophet (pbuh) and his best friend's daughter - whom he knew from her birth - was not pedophilic at all, but a very sincere and deep mutual love. The fact that he may have engaged her at the age of 6 was not at all unusual - many children were engaged at birth. The physical marriage when she arrived at puberty (which for girls can vary, and is normal, between 9 and 18ish) was also normally accepted. Most of his companions had similar marriages, as did the Virgin Mary and Joseph. According to the Protevangelion (Gospel of James), Mary was 12 and Joseph around 80 - with an already existing grown-up family! He certainly died not long after the marriage, and there is no further Gospel mention of him.
"The fact that the Prophet (pbuh) dreamed about Aishah is nothing suspicious - there was no suggestion whatsoever in the hadith that the dream was of a sexual nature, just that they were destined to marry. So, to get back to your opening paragraph, yes - it was all normal."