He's off to a good start.
1. Lift and thrust -- instead of pausing and then having to initiate movement from the top of the lift, he should begin forward movement during his leg lift with the goal of getting his hips as far ahead of the rubber as possible by the top of his lift. Currently, he is straight up over the rubber at the top. Some coaches prescribe to not starting forward until at the top of the lift. I'm not one of them. I believe it makes it more difficult to time the portion of your delivery that is between hand break and foot strike and also robs a lot of velocity in youth pitchers.
2. Hammer down--follow through with trunk flexion. He currently finishes very high. He should keep is back straight and be bent forward at the waist over his landing leg. At the end of his follow through, his shoulders should be at approximately waist level and his back should be flat.
I like a lot of what I see in the delivery right now including that he's pitching from the stretch even though he doesn't have to. I think these two things will help him have a more aggressive and high-powered delivery.