Lots to correct IMO.
For a young player, his mechanics are far too complicated. Turning and pointing his knee to second base (Johnny Cueto) adds a ton of mechanics. Lots of mechanics means lots can go wrong. It does not allow him to start to shift his hips towards the plate, thus keeping him in a straight up and down position, verses starting to drive forward. You can see at about the 10s mark just how up and down he is. He does not drive his front side, he is simply turning back towards the plate.
His front side is a bit of a mess. His lead hand (glove side - for direction) is pointing at 1st base as he starts his pull. His glove, arm and at minimum his elbow should be more pointing towards the plate and not 1st base. You can see this at the 13s mark.
He bring the ball directly above his head during his stride and his hand is facing towards first base not away from him and point the ball more towards 2nd. This, along with his front side not going towards the plate, is going to have him trying to catch up and leads to what you see at 16s mark. Elbow is way out in front of his body (leading with elbow) as he throws. He thus throws across his body, as you can see by how he finishes. At mark 22s, look at his glove hand, way behind his body and he is not finishing his motion at all.
Watch from 17s to 27s in the video. As he completes his pitch he stops his body (no more forward motion) and he actually goes backwards and off to his left hand side.
In my opinion… you have a bunch to fix. Don’t let him get comfortable in that motion for too long because breaking some of these habits will take a ton of time if you ever can fix them.