I don’t have the reference but I am certain I have read this somewhere in our history books. A fact which is conveniently ignored if one relies solely on the hadith regarding this matter. The Prophet SAW proposal for Aisha RA was not the first one. So the Prophet SAW marriage to Aisha RA did not even set the norm for this in the Arabian society of centuries ago. In fact the Prophet SAW in all his endeavors always kept the cultural norms of his society abreast and leveraged them to the extent possible to further the propagation of Islam. The only problem we have is in our historical literature we do not have other recorded examples of marriages within the same age group as Aisha RA but it is quite well-known that young age marriages were a norm of the society centuries ago and not just in Arabia.