All depends on the kid......Every kid will find trouble, find out how fast it will go, the question is where.
My oldest son is 17 and I won't let him get his permit. He's not responsible enough to earn it. I'm not going to just give it to him. He can get it on his own and buy his own set of wheels next year when he's 18.
If my younger son (now 9) stays on track, he will have some help getting his 1st car and be permitted to get his license. I fully expect that we'll throw some shiny parts at it and run it at the track.
What is too much? Nothing as long as it's used safely.