My son is 13 years old and 5'8'. He is growing rapidly. Has experience riding his friends 1984 kd80. (a relatively small bike) He pushes the little 80 as hard as it can go. He has saved up about $900 for the bike itself. We are looking for something that he can ride comftorbly at first but grow into. The bike will be ridden mostly on trails, with occasional high speed runs. He can do basic maitenance himself. He is not a newb rider, he knows how everything works, can shift with ease. He wants a kdx 200-220 and I think it is a perfect bike. What do you guys think? I heard the kdx has more bottom end power, which makes it great for trails. What bike would suit him perfectly?