The ages that you are using come from Islamic hadith (Sunni hadith). It is generally supported without question by those who follow Sunni Islam because many support (to the extent of cannonizing) the Bukhari and Muslim collections.
Being a non-Muslim there is no reason for us to base Aisha's age only on them.
Both the Bukhari and the Muslim hadith collections place Aisha both at 9 and at much older than 9 when the marriage was consummated.
Both Muslim and Bukhari state that Aisha rode with Muhammad in the Battle of Badr in 624. We see this in the Muslim Hadith collection Book 019, Number 4472. And from Bukhari Volume 4, Book 52, Number 131 we know she was at the battle of Uhud. Badr especially started off as raids and weren't planned. In order to go on a raid or to ride with the men you must be at least 15 years old, so claim both Muslim and Bukhari collections. These can be found in Bukahri Volume 5, Book 59, Number 423 and in Muslim Book 019, Number 4466. Both show that there were age restrictions when it came to riding with the parties. If this is the case, then Aisha must have been at least 13 years old when she was married in 622.
Finally, Bukhari Volume 6, Book 60, Number 399 states that during the revelation of the 54th Quranic verse Aisha makes the statement that the revelation came when she was a playful little girl. The 54th Quranic sura occurred no less than 9 years before 622. Which would have made her older than 9 upon marriage and even older upon consummation.
What happen then? Why the difference?
Back when these hadiths were collected and written down sometimes it was common (as we see with other hadiths in these collections) for the first digit of numbers to be left out when it is known. For example 16 would have become simply 6 and 19 would have become simply 9. An easy translational mistake and if this is accepted then it fits in with the other hadith of the collection.
We see it happen in the Night of Decree where 1 was used for 21 and where 5 was used for 25. It was not an uncommon practice. That may not be the reason, it is simply something to consider. Another thing to consider is the fact that these hadith collections were gathered over a hundred years after the events took place.
Also, both Hisham and Tabari (authors of two of the earliest biographies of Muhammad, next to Ishaq's whose original work has been lost) both claim that Aisha was older than 9 upon consummation.
Tabari says that Aisha was already at a marriageable age in the year 615 before Bakr's immigration to Ethiopia. This means that she would still be of suitable age in 622 when she married Muhammad. Tabari also said that Aisha converted to Islam before Umar did, which means that Aisha had to have been old enough to make such a decision on her own (aka she was old enough to talk) around 610 a fact which Hishram supports.
Also, Hisham states that Aisha was born before the year 610. Which, at the very least, would have made her twelve in 622 when she was married, and older when it was consummated.
Also, having sex with children before they hit puberty would have gone against custom and there would have been little reason to do so (see the maturity requirement found within the Quran in sura 4:5-6, and the permission custom attributed to early Islamic union and referenced by Mishakat al Masabiah).
It is also widely accepted by historians that Aisha was only 10 years younger than her older sister. At the time of Aisha's marriage, Asma was 28 years old which would have made Aisha 18. Bukhari, Hisham, Tabari, Hajar, Humbal all contradict one another on Aisha's age and Hisham and Tabari contradict themselves in this matter.
The simple fact is that we have more historical evidence that suggests that Aisha was perhaps much older than 9, than we do which suggests that she was that young. It is possible that she was younger, but unlikely, this is mainly believed by Muslims who take Bukhari and Muslim as literal canon, when studied from a secular point of view though the evidence against such a notion is quite large.
Once again the simple fact is that we don’t know how old she was, and the only reason for assuming that she was so young is either because of emphasized support of the Bukhari and Muslim collections, because you don’t know much about the early Islamic biographies (which is perfectly fine, why would you?), or because you simply want to focus on the young age since it makes Muhammad look like a pedophile.
