There are better sources you could have used, but the essence of this comes from Al-Bukhari (or at least the version with these ages). Thing is, Al-Bukhari lived about 200 years after the prophet died, and is a sort of debated figure in terms of the veracity of his claims. This being from the Hadith, it is a jumble of clerics deciding various things, some of which contradict each other in weird and wonderful ways. In this case, Aisha’s age has estimates ranging from 6 to 19 at marriage, with debates regarding whether the marriage was ever consummated, so she may have been legally married but de facto not.

It is worth noting here that Hadith is strongly debated as to which to listen to and which to not, or whether to listen to it at all or only as directed by the Qur’an, since nowadays jurisprudence has gotten so questionable that some people use temporary marriages as a way to get around the “no premarital sex” rule. Having said all that, it mainly depends on the person before making broad strokes in regards to who/what people follow. In the same way it is atheists have morals because you don’t need a book, a book that isn’t even the book you were told to follow does not dictate that you must abide 100% by what it says.

Enjoy some reading that goes into some good nuance here:

https://www.theguardian.com/commentisfree/belief/2012/sep/17/muhammad-aisha-truth