Considering he's only 18 (at least that's what they say he is- there's a bit of speculation that he may be a few years older), he might still grow. Add a couple a few inches and maybe he can dunk by tip-toeing.
He still has a lot of ways to go though. Reggie Evans is like 2 times better than him on offence, which is saying a lot. He can't don much else but dunking the ball.