A rationale trying to explain why Mohammed married such a young girl is given in Sahih Muslim vol.2 footnote 1859 p.715. It says that \"it was some exceptional circumstances that Hadrat ‘A’isha was married to the Prophet… The second point to be noted is that Islam has laid down no age limit for puberty for it varies with countries and races due to the climate, hereditary, physical and social conditions.\" They also mention support from the disreputable Kinsey report on Sexual Behaviour in the Human Female