The bike really depends on how old he is and how tall he is. My son rides a CRF150R. It is a fast bike. He started off on a CRF100. He has friends his age that are riding everything from a CRF110 to 125s. He is on the biggest bike of all of them.

I prefer a 4 stroke. Unless you can turn wrenches and he is going to be riding all the time, you don’t want a 2 stroke. A 2 stroke doesn’t like to sit.