To do tricks and stuff (manuals and especially street stuff) I find being big (6'5 and 260) to be a disadvantage. I am not sure exactly why but I chock it up to centre of balance and pure size. In order for me to manual I really need to be off kilter...small guys work it better. If you look at most (not all I do know about the odd freak) pros they are small guys. When I was at the freeride comp in whistler I had a chance to meet most of the best riders in the world. Let me tell you there was no big freeriders at all. In fact small would be generous for quite a few.

Now to throw in another caveat. I do know there are guys like roxwell (the tall dh guy) and a couple of bmxers who prove this wrong but typically shorter riders do better on the technical end of riding (that and they tend to look smoother)

Now...practice does make perfect and he can get really smooth especially if he is young...has he ever tried a BMX...it helped me a tonne and I just started riding them at 28/.