I recently turned 16, and yet my penis still seems smaller than I'd expect. When it's normal, it's usually between 1.5-3 inches, and when erect it can be up to 5.5-6. Is this normal? I think I hit puberty late, as I did not have hair under my armpits until about a year after some of the other boys.
You are bigger than average for an adult male - 5.1" erect. Flaccid size varies considerably.
It can still grow too. Your penis can grow into your early 20's.
Hope it helps.