The boost of hormones thing is interesting. I wonder quite a lot how big my penis would be if I was full term and not 12 and a half weeks early. Maybe my I'll still grow, but my thinking was that being born premature, I would develop later, because I missed development as a foetus. Yet I matured around 12 or 13, like everyone else. So it does seem like I'm fully grown...

I also think if I had a son and he was bigger than me then that would be proof that proper and timely development in the womb is a factor. Anyway I spose it is majorly and mainly hereditary, penis size...