As this was his (description), it was not desirable.
But this is not how it was, according to what was related by Allah Almighty: "But if the right is on their side, they come to him with all submission" [Qur'an ].
For it is not permissible unless he believes that her best-interest requires it, and God is his judge on that.
At the time in which we see our children now, with the number of illiterates, they stay in school until their tenth year.
It used to be that the child, male or female, would memorize the Qur'an before reaching their ninth year, and would memorize Arabic poetry and prose.
The Qur'an is not like the books of jurisprudence which mention what the implications of things are, even if they are prohibited.
It is true that the prophet (PBUH) entered into a marriage contract with 'A'isha when she was six years old, however he did not have sex with her until she was nine years old, according to al-Bukhari.