Other than the obvious fact that if you start training when you are 14 you have a lot more years of training to build on? Is there any correlation to the growth of the body (muscles and final bone size) during these teen years with resistance training vs a lifter who starts lifting in his mid 20’s lets say?
Not really, no.
Not that it’s evidence based but my n=1 opinion about it:
Background: I’ve been skinny as hell well into my twenties until I’ve started training and gotten from 60kg to around 85-90kg now. I’ve put on quite a bit of mass but I’m still looking relatively small compared to other trainees of my height because I just have a small frame.
Now here’s the funny part, my build is still super slim (narrow hips, narrow shoulders, thin wrists and ankles) and this causes some issues: I walk like a damn heavy weight bodybuilder even though I’m not. My thighs are rubbing against each other, my arms are flaring out to the sides because they’re touching my lats… but there also some more practical issues if you will, like having stability issues with holding heavy dumbbells properly because I’ve gotten stronger from barbell benching but my hands and wrists are still damn small. Also due to my feet and ankles being relatively small they give me issues when hiking, running etc. in the sense that they tire very very easily. The funny thing is: they didn’t use to tire when I was lighter in weight.
Now this is entirely speculation but I think that would I have gained some weight in my teens (so not necessarily muscle mass) my ankles, hips, wrists, feet, etc. would have grown proportionally to properly support the weight as the bones would have reacted to the stress of being heavier. And this on the other hand would have probably allowed me to put on more muscle mass using barbell training and thus getting stronger than it does now.