WTF?! 15 years old?! That's incredible..Supposing he was 5'9 at 15, that's amazing. True athlete right there.
One of the guys in my gym class in high school was on the basketball team. He was 5'7" and could dunk. About all he could do, but that is besides the point. Vertical leap can be trained, but some people do have "natural" ability and can just do this stuff.