Lots of good advice above from experienced people. If you have been reading the board for awhile, you have read all of above before. And it is all good advice.
To what you (your son) should be focusing on? Health first and foremost, combined with strength, mobility and conditioning. My recommendation is to go to Eric Cressey or an Eric Cressey like experienced PT / CSCS that has a lot of experience with pitchers. Get your son a movement assessment and a bio-mechanical assessment and a written program from the trainer. Driveline Baseball is another, as is Rockland Peak Performance.
I say all above from reading, not from personal experience. I am trying to figure out what is the best next step for my son, a 2020 RHP. No injury or soreness, it just seems like the next step. And an expensive step. And a harder sell to my son, who would rather be competing in the summer than on a program.