Interesting point.
One wonders if you think same point applies to Aisha being 9?
If not, why not?
Aisha is a very politicised figure in the early history of Sunni/Shia differences and is pretty much despised by many Shias. She was aligned with the Umayyads, who won out over the backers of Ali and started the Umayyad dynasty.
Under the Umayyad Caliph Abd al-Malik is when lots of clearly 'Islamic' things start to enter the historical record (inscriptions featuring both Muhammad and God, rather than God for example), also the Dome of the Rock and its Quranic inscriptions (well they don't quite match the contemporary Quran but pretty close).
So it seems like a reification of Islamic identity was happening around this period, and subsequently a (proto)Sunni identity began to emerge, and elsewhere a Shia identity.
Unless you assume that the hadith tradition flawlessly recorded objective history then it would be reasonable to assume that Aishas backstory has been shaped considerably in order to support the political needs of the Ummayad and Sunni communities.
As for her age, no one knows. Early Muslims weren't that good with dates. According to various Muslim
sources Muhammad
"was born in the Year of the Elephant, or fifty days after the attack of the troops of the Elephant, or thirty years after the Year of the Elephant, or forty years after the Year of the Elephant Many traditions are recorded in Ibn N~ al-Din's Jami' al-iithiu, fols. 179b-180b:the Prophet was born in the Year of the Elephant, he received the Revelation forty years after the Elephant (The fight at - K.) 'Ukaz took place fifteen years after the Elephant and the Ka'ba was built twenty-five years after the Elephant; the Prophet was born thirty days after the Elephant, or fifty days, or fifty-five days, or two months and six days, or ten years; some say twenty years, some say twenty-three years, some say thirty years, some say that God sent the Prophet with his mission fifteen years after the Ka'ba was built, and thus there were seventy years between the Elephant and the mission (mab'aJh) of the Prophet; some say that he was born fifteen years before the Elephant, some say forty days or fifty days, some say thirty years before the Elephant, and finally, some say that there were ten years between the expedition of the Elephant and the mission"
(I post this source all the time but it is the best, concise example of how little early Muslims agreed upon. Tradition becomes more standardised, and also more detailed, the further it gets from the time of Muhammad.)
It's quite possible her age was politically expedient to both prolong her time with the Prophet to help establish her status as his favourite wife, and also to guarantee her chastity at marriage in response to Shia attacks on her virtue. Ultimately the only things we know about her are from the Islamic tradition so if you consider that unreliable then you are just left with speculation.
