Regarding velocity, I think I’m seeing hips and shoulders rotating together instead of hips before shoulders. I’m having a hard time seeing much hip and shoulder separation which is where most of a pitcher’s power comes from. But, I’m a firm believer in cleaning up the earliest parts of the delivery first so I wouldn’t work on this just yet.
I agree with the others on coming set with the feet closer together to eliminate the weight shift towards 2B before moving towards the target.
Also, watch the path his head moves at the beginning of the delivery. After the weight shift towards 2B, his head drops quite a bit before moving towards the target. This is wasted movement that makes him slower to the plate. And it wastes energy by directing some into the ground as he has to exert force downward to stop the drop. I would have him come set with some bend in the waist and knees to get him closer to having his head move only forward.
I also agree with the recommendation for the Hershiser drill plus I’d add in the cross-over drill. Search YouTube for these drills - they are Tom House/NPA drills. These drills will help him not only move forward sooner but will also help him lead with the front hip more through the early part of the delivery instead of opening up and reaching with the front leg/foot.
Work on these things for awhile and then see what effects they have downstream in the delivery.