I was definitely a late bloomer. Had a VERY small penis until I was about 16, and didn't get any pubic hair until I was 14. That left me with the sad situation of gym locker rooms where everyone looked huge and hairy, and I looked very young and feeble. It really made me feel inferior to everyone else and made me avoid going too far with any dates, well into my early twenties.
But somewhere along the line even as I still felt self-conscious about it, my penis just got bigger without me really noticing. I was in Europe with a girlfriend when I was 24, who saw me naked and commented how big my penis was compared to her previous boyfriend (nothing else happened with her). That was the first time I felt "big". Just recently a longtime friend of mine sort of "witnessed" me in the gym showers and at that point I decided that I am above average, enough to take notice (as if it matters so much LOL). I talked about that in another thread.
Now I'm in my early thirties, and my wife always comments how big I am (I guess she has to say that, right?), and we have our first child on the way. So those early and VERY HARD days of feeling inferior, have pretty much been put away. But maturity would dictate that, I should have felt confident with myself no matter what penis size I have, and that is a lesson I wish I realized in those days.