Chris Mc,
Re the issue of "doing weights" as a 15-17YO - IIRC - it seemed to be more of an issue with doing "unsupervised" weight training, possibly aiming at "improving" the "pretty boy" muscles etc. Again, I am reasonably sure that there was a place where doing weights was relevant, and indeed, helpful, however, I believe that there were many who thought "too much, too soon" wasn't a great thing ( myself included, as aa mere parent, with absolultely no relevant knowledge pf the benefits - or pitfalls!).
As to the possible negative effects, particularly where young boys were going through "growth spurts" - from personal experience ( 2 sons etc etc ....)we were on the receiving end of back &leg injuries, which we suspect the weightlifting bit contributed to.
Fortunately, their teachers/trainers recognized the issues reasonably promptly, and training regimens changed ( for the better, I believe)
Thankfully, both young men have survived - and still play a bit of rugby here and there.
Conclusion - (a personal observation, naturally) - it has a place - but only in a well controlled / supervised environment - and for the right reasons !
Cheers
The Hound