There is material from both these hadith writers and earlier Islamic histories suggesting Aisha must have been older than nine when married.
* According to hadith in Bukhari and Muslim, Aisha is said to have joined Muhammad on the raid that culminated in the Battle of Badr, in 624 CE. However, because no one below the age of fifteen was allowed to accompany raiding parties, Aisha should have been at least fifteen in 624 CE and thus at least thirteen when she was married following the Hijra in 622 CE.
* Ibn Hisham’s recension of Ibn Ishaq’s Sirat Rashul Allah, the earliest surviving biography of Muhammad, records Aisha as having converted to Islam before Umar ibn al-Khattab, during the first few years of Islam around 610 CE. In order to accept Islam she must have been walking and talking, hence at least three years of age, which would make her at least fifteen in 622 CE.
* Tabari reports that Abu Bakr wished to spare Aisha the discomforts of a journey to Ethiopia soon after 615 CE, and tried to bring forward her marriage to Mut`am’s son. Mut`am refused because Abu Bakr had converted to Islam, but if Aisha was already of marriageable age in 615 CE, she must have been older than nine in 622 CE.
* Tabari also reports that Abu Bakr’s four children were all born during the Jahiliyyah, the pre Islamic period, which could be said to have ended in 610 CE, making Aisha at least twelve in 622 CE.
* According to Ibn Hajar, Fatima was five years older than Aisha. Fatima is reported to have been born when Muhammad was thirty-five years old, meaning Aisha was born when he was forty years old, and thus twelve when Muhammad married at fifty-two.
* Most of these narratives are reported only by Hisham ibn Urwa reporting on the authority of his father. All the narratives of this event have been reported through narrators from Iraq, where Hisham ibn Urwa is reported to have shifted after living in Madinah for seventy-one years. It is reported in one of the most well known books on the life and reliability of the narrators of the traditions ascribed to the Muhammad reports that Yaqub ibn Shaibah said, “narratives reported by Hisham are reliable except those that are reported through the people of Iraq”. It further states that Malik ibn Anas objected on those narratives of Hisham, which were reported through people of Iraq. Another book on the narrators of the traditions of the Muhammad reports that when he was old, Hisham’s memory suffered quite badly.
* According to the generally accepted tradition, Aisha was born about eight years before Hijrah. However, according to another narrative in Bukhari (Kitaab al-Tafseer) Aisha is reported to have said that at the time Surah Al-Qamar, the 54th chapter of the Qur’an , was revealed, “I was a young girl”. The 54th Surah of the Qur’an was revealed nine years before Hijrah. According to this tradition, Aisha had not only been born before the revelation of the referred Surah, but was actually a young girl, not even only an infant at that time. So if this age is assumed to be 7 to 14 years then her age at the time of marriage would be 14 to 21.
* According to almost all the historians, Asma the elder sister of Aisha, was ten years older than Aisha. It is reported in Taqreeb al-Tehzeeb as well as Al-Bidayah wa al-Nihayah that Asma died in the 73rd year after migration of Muhammad when she was 100 years old. Now, obviously if Asma was 100 years old in the 73rd year after Migration to Medina, she should have been 27 or 28 years old at the time of migration. If Asma was 27 or 28 years old at the time of hijrah, Aisha should have been 17 or 18 years old at that time. Thus, Aisha - if she got married in 1 AH (after Migration to Medina) or 2 AH - was between 18 to 20 years old at the time of her marriage.
* According to many Ahadith in Bukhari, it is believed Aisha participated in the battle of Badr and Uhud.Also in Bukhari (Kitabu’l-maghazi) Ibn `Umar states that the Prophet did not permit me to participate in Uhud, as at that time, I was 14 years old. But on the day of Khandaq, when I was 15 years old, the Prophet permitted my participation. So if it was not allowed to participate in Uhud for people younger than 15, then Aisha would be atleast 15 in those battles, making her age atleast 13 to 14 at the time of marriage.
* Tabaqat ibn Sa’d, 8:58; Ansab al-Ashraf, 1:410. Opinions are in disagreement concerning her marriage with Muhammad. Their marriage seems to have taken place either two of five years after the Migration (Usd al-ghaba, 5:501).