Weighted balls are ok to use as part of an overall strength and conditioning program, but they're better used as something to augment a strength and conditioning program and not as a primary function. When those male hormones really kick in, there can be some amazing changes.
Agree with Truman. Weighted balls should be supplementary to strength & conditioning basics - squats, deadlifts, power cleans, plyometrics - as long as someone can show him how to safely and properly execute those movements. Then, as he builds up a strength base, add in the weighted balls.
I see you are doing Jaeger-style long toss. I'm a big believer in that for arm health.
I've never done a weighted ball program, but it's hard to argue with the results at Driveline. The research they do at their facility is phenomenal.