I never do dips anymore but it's mostly due to shoulder issues. Nearly every credible S&C coach that I've read about or talked to in regards to dips seems to think that the exercise is only good for people with extremely healthy shoulders. Obviously, they can cause a great deal of stress on the shoulders. This is actually the first time I've heard about the sternum issue with young athletes... but to be honest, having Mark Rippetoe AND Dan John warn against them is a pretty good reason to be, at the least, overly cautious with them. I personally, don't feel that dips are that great anyway. Yes, they can build a lot of strength... I won't deny that. But there are a lot of other exercises that can build that strength as well and dips aren't exactly a natural movement. I can't think of do many situations in real life or sports were you would be pushing in that position.