Critics allege that Aisha was just six years old when she was betrothed to Muhammad. They base this on a saying attributed to Aisha herself (Sahih Bukhari volume 5, book 58, number 234), and the debate on this issue is further complicated by the fact that some Muslims believe this to be a historically accurate account. Although most Muslims would not consider marrying off their nine-year-old daughters, those who accept this saying argue that since the Qur'an states that marriage is void unless entered into by consenting adults, Aisha must have entered puberty early.
They point out that, in seventh-century Arabia, adulthood was defined as the onset of puberty. (This much is true, and was also the case in Europe: five centuries after Muhammad's marriage to Aisha, 33-year-old King John of England married 12-year-old Isabella of Angoulême.)