Driveline is the by far and away the best program out there. Science driven and cutting edge all while being affordable and approachable. There are a lot of imposters out there who claim a lot of things that just aren't true. But I can tell you first hand that Driveline is the best way to go. A lot will depend on the amount of work your son is willing to put into it but if he is motivated to do so (and my son was willing to work for it) then you can't beat Driveline.
Texas Baseball Ranch is a great place and Coach Wolforth is awesome. Very expensive and not quite as approachable as the guys at Driveline. But a great program, nonetheless. I think the Ranch does a great job on arm care and provides some great instruction, but again, it's pretty expensive.
My son started with the Ranch at about 13-14 yrs old, but moved to Driveline and really liked it and still uses their training methods in his college program.
And don't believe the naysayers out there about Weighted Ball program. Driveline has some great articles like this one https://www.drivelinebaseball....upporting-their-use/ that detail a new study at ASMI that show they are a great tool to help with building velocity.
You will hear a lot of different opinions about how best to safely train and build velocity. You will also run into "pitching coaches" who don't really know anything about how to safely train. Sitting on a bucket while your kid throws a bullpen to him doesn't make him an expert. My son and I made sure to educate ourselves so we could form the best decision on which program worked best for him. I would also recommend reading the book "The Arm" by Jeff Passan, which is one of the best ways to educate yourself on the the risks to young pitchers.