In preparation for the Olympics, ABC Nightline did a special on body building by young men, especially one teen (David Laid) who started at age 14, and is interviewed at 18. But another body builder developed organ failure problems (but that would happen with steroids). Here’s the ABC Nightline link.
I’m reminded of a kid (Hugo Cornelier -- is that French Canadian?) who took a selfie everday from age 12 to 20. There is a noticeable difference.