It's a different rulebook, you have to realize this is a video game and not some real life fiasco that ruins his life. Banning somebody from playing your video game isn't a crime, don't treat it like it is.
Also, it's Valve's TOS, like i said, it's a video game. They have the right to ban people, who break their terms of service, regardless of age. You realize the minimum age is 13 at the time, he already broke one rule by being 12.
I'll be BLUNT with you. PLAYING A VIDEO GAME, IS NOT A RIGHT, IT'S A PRIVILEGE. The fact you can make a "Career" out of it, is coincidental. But it's still just a video game, these guys aren't athletes, most of them have never even gone to college. The only people who skip college are the legends of normal sports, these kids just don't want to go to school lmao.
Also, here's something to clear up your mind.
If nobody saw you run a stop sign, do you get a ticket?
No. Can't ban what you can't see, I don't disagree, I'm sure other people have broken the rules, but they just weren't caught, and that just isn't preventable lol, trying to monitor MILLIONS of users.