Can anyone tell me how true/accurate this is?

I read a research paper that said h*beph*lia is not abnormal saying that across history/cultures, the most number of marriages happened with girls 12-15 and men 19-21

However I read other sources saying while true, relations happened around 15+ as having a child at an early age was pretty harmful and dangerous and stuff with people under was infrequent/not common or the norm

So is this correct?