How does the coaching staff react to his work? Do they share in your insight and concern?
Be careful giving advice here. Yes, it's constructive and helpful at times - BUT, sometimes there are other agendas just waiting in the wings that can pop up at the worse time and boomeranged back on you.
Coaching amateur pitchers requires more than just advice about - this and that. There are compounding components that can double-up on a pitcher, one causing a greater problem then the other and so forth. And if that wasn't enough, giving a teammate advice involves a lot of unknowns. Unknowns like his conduct off the field, his health habits, his eating and nutrition habits, and other personal conduct. Another field of land mines can be your teammate's social experiences and his interaction with others like friends and family.
In any event, I'm sure the suggestions and observations here will be sound and valuable. In fact, as a starting point, advise him about this web site and suggest that he join in.