I take the criticism on extrapolating from girl’s age to what was a norm. Indeed, we have yevamos cases of groups of brothers and corresponding sisters, dying one after another that are hopefully not daily occurances.
Still, you can look at a variety of cases and get a feeling when a case is a stretch case or reasonably a norm – in the latter case, it is discussed in many situations, with practical details.
So, my feeling is that pre-12 y.o. marriage was not that typical, while possible, but 12-13 bogeres
was closer to the norm. See multitude of cases discussing 12-13 y.o. naara/bogeres engagement issues. Another example – when father sells his daughter into servitude (not that typical), she is expected to be married or go free at the bas mitzvah (as this wold be a typical moment).
Also, a notion that a man should not live/visit too long at his in-laws before of mother-in-law there. This hints that husband and bride’s mother are typically close to each other in age. Would not be such a big issue if hatan is 15 and MIL is 40 …