Gonna have to go ahead and second Obea Moore on this one. I haven't read the whole thread, but I'd be surprised if he hasn't been brought up a dozen if not a few dozen times. It probably cannot be reiterated enough given the thread title.
Granville came to mind, too, but it wouldn't be accurate to say he did nothing in college. I remember running summer track and reading about all of Obea Moore's records. It seemed like he held every record from 200-800 in every age group. I'm not sure what's more impressive, the range or breaking 46 when you're 16. I had to check, but he still holds about a half dozen records. Seeing it on paper is one thing, but I actually got to see him run once. I'm in my early thirties now and it was nearly twenty years ago, but I still remember pretty vividly the utter domination. I'm as much a fan of football as track and I'm not sure I've seen anything like it in any sport at the youth level to date. It would be like someone scoring every single time they touched the football.
It was something to see, but now when I think of it, he was truly great for any age, but it is sad how early he peaked and how burnt out he was. Same applies to Granville. Even being that talented, they probably shouldn't have been running that fast at that age without sacrificing the future. Expectations got built up too much for a kid to handle, not just physically but mentally. I want my kids work hard and compete to an extent, but if you're good and have potential, it's not like it will be a big secret. Take your foot off the pedal a bit and save some for when it counts or when they're mature enough to handle the pressure. But he was something special even though he never did anything after high school and I'm glad I got to see it.