Until 2002, the age of marriage for a girl in Iran was 9. Now it's 13.
http://www.sltrib.com/2002/jun/06242002/nation_w/747915.htm Hard line Muslim clerics object because Muhammed married a 9 year old girl. Traditionally Muslims marry a girl as soon has she has her first menstrual period, so if she menstruates early, she can be married early.
Or, as some say in the West, "if she's old enough to bleed, she's old enough to breed."
Not that I agree with this at all, just observing that not just Muslim men want to have sex with underaged girls, but our religion and culture doesn't allow it, and theirs does.
I have seen thirteen year old girls who looked incredibly mature, but never a nine year old. Still, every so often one does read of a very, very young girl who is pregnant. As a woman, I think it's weird - I feel zero attraction to pubescent boys.