First: That mound is kind of small for kids his age. A pitcher should never step from slope to flat.
Lots of good stuff there in his mechanics. He definitely tries to throw hard, and that’s good. He’s a bit deliberate at the start, however, and that can get worse as they get older. He’s getting no benefit from throwing wind up. He’s essentially throwing from the stretch due to his free foot step. With a step like that, just have him throw from the stretch. It will get him to the plate faster and give the hitter less time to settle in.
He’s a bit too closed at the start with his shoulders where he would be better off simply being aligned with the target. If he decides to start from the stretch, he can simply come to set with a slightly closed free foot which will keep his hips closed–which is what really matters. This will improve his already decent hip/shoulder separation and make him more powerful.
Finally, he tilts his shoulders a bit–not severely, but a little–to the first base side and he needs to have his head and eyes more level with his shoulders. It will help him maintain balance easier and keep more body mass along the target line and give him a touch more velocity.
Overall, no really serious flaws. Just a few tweeks to boost his MPGs and MPHs.