On page 69, it says that he was married to her when she was 9 years old. Between 621 and 623 Asiha is said to have contracted a disease whereby she temporarily lost her hair. She could not have been more than 10 years when she went to live in Muhammad's house. The fact that she took her toys with her to her new home indicates that she was psychologically and socially still a child. I am sure she would have been able to recount accurately as to when and where she got her first menses.
Most girls do remember such events rather accurately.
He was to use a similar tactic when he wanted to marry his step son's wife. I do not see, but, that your Lord hurries in pleasing you. Muhammad wasted no time in realizing what he had been dreaming. Here it does not seem that Abu Bakr consented to the marriage wholeheartedly. Muhammad's infatuation and relationship with Aisha fits this criterion.