There is a lot to like about this young man's delivery and no big, obvious problems.
I do agree with jd's opinion about the importance of starting posture; that is, whether in the set position or starting from the wind-up, your son should try to learn to be consistent in the placement of his feet (no more or less than about shoulder width. The reward for doing this comes pretty quickly--a more repeatable delivery leads to better control of the strike zone.
If you look at video of sequential deliveries by most pro level players, it is astonishing how "machine-like" they are in terms of consistently repeating their starting posture....pitch after pitch after pitch.
You can see the result of their initial precision played out in the rest of their delivery...when they are "on", most good pitchers will repeatedly land on the same cleat marks with their stride foot. If their delivery includes a "drag line" made by the post foot during the delivery, then that will also repeat identically from pitch to pitch.
Finally, I agree fully with jd's last sentiment: He's looking good, and should be having a lot of fun.