.
Most of the narratives concerning this issue printed in the books of Hadith are reported by one Hisham ibn Urwah. (A single source for ALL - Ideally, the Muslims look for two, three or four sources for reliable narrations)
It is strange that no one from Medina has reported on this issue where Hisham lived the first 71 years of his life, and where his pupils included well-respected people like Malik ibn Anas.
After age 71 Hisham moved to Iraq. Tehzibu'l-Tehzib, one of the most well known books on the life and reliability of the narrators of the traditions of the Prophet (pbuh)reports that according to Yaqub ibn Shaibah, his (Hisham's) narratives are acceptable except when he narrated after moving to Iraq." It is reported that Malik ibn Anas, Hisham's own pupil in Medina, also objected to Hisham's narrative from Iraq.
My note: Almost every report of Ayesha's young age goes back to Hisham bin Urwa from the time when he was old and possibly senile. Secondly, even his old pupils, like Malik ibn Anas rejected his narration of that period. Likewise in the 15th century many scholars rejected the narrations of Hisham from his old age.
Al-Tabari says, "All four of Abu Bakr's children were born of his two wives during the Pre-Islamic period" (Tarikh'l umam wa'l-mamlu'k, Al Tabari (died 922), Vol 4, p.50, Arabic Dara'l-fikr, Beirut, 1979)
Tabari also states that Ayesha was born in the period of Jahiliya (Pre-Islamic period) (In other words in 610 CE or earlier) Even if she was born in 610, she would be 14 years old when she began living with the Prophet. Amazingly, Tabari in a different place then goes and quotes Hisham ibn Urwah that Ayesha was nine when she started living with the Prophet!!! (Not a very scholarly work, is it?)
There are multiple accounts of Ayesha participating in the battles of Badr and Uhad. At the same time, Bukhari (in Kitabul Maghazi, Bab Ghazwa-i-Khandaq) narrates, "Ibn-i-Umar states that the Prophet did not allow me to participate in Uhad because at the time I was 14 years old. But on the day of Khandaq (next battle), when I was 15, the Prophet allowed me to participate.
Ayesha's participation in battles of Badr and Uhad clearly indicates that she was not 9 year old, but at least 15. Dr. Shanavas adds, "Women used to accompany men to the battlefield to help them, not to be a burden on them."
Sura Qamar: Ayesha is reported to have said that she was a young girl (jariyah in Arabic) when sura Qamar was revealed. Sura Qamar was revealed eight years before Hijra, in 614 CE. If Ayesha started living with the Prophet at age 9 in 623 CE, she should have been a new born (sibyah in Arabic) when Sura Qamar was revealed, not a jariyah (a young girl). assumed to be somewhere between 6-13 year old. That would suggest Ayesha's age at the time of marriage to be 14-21 years