What would have been the accepted age of sexual maturity in Rome? Would it depend on the man's age? How would it have compared to that of other countries, or even other regions of the empire?
I can't speak to a broader context, but the legal age of marriage in Rome was 12, and, according to the marginal notes in my copy of the Confessions, his fiancee was 11 at the time he broke the engagement. Sorry I don't have a specific source to point you to!
The legal age for marriage was 12 I believe. Most women got married between 12 and 16. This was the standard age for marriage in other cultures as well, for example the Jewish culture, so the Virgin Mary is believed to have been around 12 years old when she bore Jesus.