Child marriage

Hello Rabbi Michi!
How are you doing this week of psychometrics (at least for me)?
I recently saw a tweet from someone saying that Jews say that Muhammad was a pedophile and then bringing up a question that was asked to Rabbi Hanoch ben Moshe (a student of Rabbi Shmuel the Prefect) about the birth of a six-year-old girl (the birth was done by mistake). Apparently her claim is that it is the same among Jews. I don’t quite understand her point of departure, but
A. Since when is there a Jewish reference to Muhammad (apart from Maimonides in the Yemenite letters)
B. Why do Jewish social norms in the 11th century change for anyone today? It was different in the Talmud, it was different during the Shulchan Arutz Sheva period, and it is different today.
I’m not that knowledgeable about minor marriage in Halacha, except that the Shulchan Aruch rules out marrying at the age of 18. I don’t know how much this happens today.
 
2. What advantages do you think a college has over a university?