Hey, let's not argue you guys...
There might be stages of puberty, but there are none that I know of yet anyway. One thing that's certain is everyone develops differently: at different rates and at different places of growth.
Puberty does in fact end in the early twenties for most guys. Puberty is generally when your sexual organs mature, and (for the guys) the testicles mature, and then they produce hormones. These hormones tell our body to grow - the production of hormones stops around 18-21ish
(these numbers are always approxomate).
This is why it's easier to buy shoes when you're of legal drinking age
So yes, cheif, your penis might grow some more. You are about average size right now so there's nothing to worry about =]