Conversation so far has been great. I'm 31. My brain feels 50 and my right arm feels 75. Been throwing weighted balls since a partial thickness tear in my cuff years ago. 
Anyway, I'd be more than happy to answer questions. Not trying to pander, but we do a lot of research and experimentation with weighted implements. Wrist weights to weighted baseballs to weighted footballs for all sorts of things. Command, velocity, etc. Weighted ball ranges from 2 oz to 2 kg with the heaviest ones being thrown all-out at 16 oz.
Skepticism is good. Who's to say a 6-8 week weighted baseball program that puts 3-4 MPH on the kid's arm was really a significant factor? What if the kid threw 6-8 weeks of the same reps, but with 5 oz baseballs instead? Could have seen the same results. Those are the kinds of experiments you should do. Hard to do with a sample size of 1, of course. Which is why I did a lot of experimentation with select teams while working for them, splitting them up into matched groups. Our research (and Dr. Coop DeRenne's research) is fairly conclusive: The stuff works better than control.
Injuries, on the other hand... 
Lots of ways that can go. Suffice to say I agree with Eric's thoughts on having a stable base of strength before engaging in an aggressive training program of any sort.