"You imply that he's a PO, and if so, he should take a few months off from throwing each year,"
A bit of thread drift, but I distinguished between throwing and pitching. My son threw virtually every day from the time he began rec ball all the way through college. Throwing conditioned his arm. We took time off from pitching each year (varying length). For him, long toss made his arm feel loose and strong; just always pay attention to form and be aware of fatigue (especially when young and mechanics are inconsistent).