According to the Sunni website Discovering Islam, Aisha was older than six years old:
We find evidence in both Hadith books and history books that indicates Aisha must have been older than nine when she got married:
According to a 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 version 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 also reports that Abu Bakr’s four children were all born during the Jahiliyyah (Pre-Islam Period), which has ended in 610 CE, making Aisha at least twelve in 622 CE.
According to the generally accepted tradition, Aisha was born about eight years before Hijrah (Migration to Medina). 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 in Ibn Kathir's 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, if Aisha got married in year 1 AH or 2 AH (after Migration to Medina), she must have been 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 both of Badr and Uhud battles. Furthermore, in Bukhari's Kitabu’l-Maghazi, Ibn `Umar states: "The Prophet did not permit me to participate in Uhud battle, as at that time, I was 14 years old. But on the day of Khandaq battle, when I was 15 years old, the Prophet permitted my participation". So, since it was not allowed for Muslims younger than 15 years old to participate in Uhud battle, Aisha, who participated in Uhud, must have been at least 15 years old in those battles; thus her age was at least 13 to 14 at the time of her marriage.
According to Shi‘i scholar Sayyid Ja'far Murtada al-‘Amili, the early historian Muhammad ibn Ishaq says that Aisha was approximately the nineteenth person to convert to Islam after the commencement of the Holy Prophet (s)’s mission. Even if she had been just seven at this time, she would then have been seventeen by the time she was married and twenty at the time of Hijra.