Take this for what it is worth (which is not much). It is also difficult to see much in low res internet video from a distance.
1. Get rid of the squat. He is a tall kid so stand tall with and get legs closer together. Looks like he is riding a horse.
2. First step back is too wide and starts to get him un-balanced from the beginning. One small 45 deg angle step to just get things moving should be fine. Stay balanced and centered over his belly button.
3. I would consider starting him from the other side of the mound for better angles to the outside of the plate for righty's and better angle for lefty's.
4. Again hard to tell but he looks like he is leaning backward which causes him to fall off to the left (his right), may also be caused by his big step to the side to start things.
5. He looks a little herky, jerky - be smooth and then explode. Since he it is his first time on the mound as a Varsity pitcher he is probably a little psyched up...
6. Biggest thing I see is a weak glove side as Trojan Skip mentioned as well as his landing on his heal. He must be locked in on the front side, head steady, and landing flat to very slightly on his toes. His glove side is falling off instead of back to his body. I suspect there is a lot of potential extra velocity left in him in with some work in this area. Actually if you get him landing properly the fall off will take care of itself.
I would add that some of this is developmental and takes time as he grows into his body. I suspect if you look at him a year from now much of this will go away. Tall kids have lots of moving parts that take time to develop.
I can't underestimate how important it is to find someone he can relate to and work with one-on-one on some of the nuances. You can post stuff here and get some basic advice, some of which will be wrong so be careful.
Nice looking boy!