As disgusting as what was alleged he did i would still agree with you that it shouldn't forbid him from ever playing professional baseball. He was a kid, and yes, of course he was old enough to know it was wrong but when your 15 you can't appreciate or understand the consequences your actions have. That part of your brain doesn't develop until your early 20's.
If he wanted to be a youth baseball coach i would have a lot of more reservations. He completed his treatment programs, paid a price and like you i believe in rehabilitation and second chances. I don't think an incredibly disgusting act when you're 15 should define you for the rest of your life. From all accounts he was a good teammate, and had no issues during his time at Oregon State.