Nice inning 8)
He has a strong upper and not much lower.
Right now is when you learn conditioning.
Make certain diet and grades are first and foremost.
He'll find more fb movement when he does "get it" with the lower half and it sync's to his top..it may drift his arm slot lower, I wouldn't worry too much if it does (Timing drives that aspect...and likely it will "find" him a nice sinker). A nice clean delivery like this is somewhat common at this age but the whole body needs to be involved; A) To increase velo and B) To handle the load of hs ball (And susequent hi level travel/showcase stuff).
Over the years it's pretty much proved itself out that the "all arm" kid is going to top at at 85 and then he'll cast around for methods to improve velo from there. Long Toss, weighted balls, "intent"..things like that will be thought about and debated...I've found that an entire body approach (Conditioning, other sports, strength training, diet, mental approach) appears to succeed when adhered to as a discipline..you may have "some" success if you choose and adhere to a single path (Most "plans" do register improvement initially) but if all aspects aren't "fortified" there will be consequences...Start with grades and work down...bad grades..no play, bad diet...conditioning fails, bad conditioning...joints fail, forget fielding...injury...no arm vitality...velocity damages..it's all on his plate...desire, determination...effort.
I suggest you get as much recorded as you can.
Have his pc develop a long term.."how do I get to...X" plan.
The crucial thing right now for him is continue to hone his art, condition, ensure that he is fully understanding about arm care, bodily vitality is key...over-all fitness not sports specific to the exclusion of everythng else.
As much competition as his arm health will allow...