Probably a good rule of thumb...but depends on the kid. I started driving when I was 12 (we were out in the country). Bought myself a '68 camaro project that ran and drove and had every bit of 300+ hp when I was 14 (for $3k), then my dad for some reason bought me a nicer camaro that I started to make fast only to sell it for my first TR when I was 15. I've seen way more adults do way more dumb things in quick cars than I ever did in any of those 15 years ago. But kids (especially now) can be insanely stupid once the pissing contests start.
I think the harm is more in the kid not respecting what they have or how much it costs, and thus not taking proper care of it. Then being entitled $hit$ till well in to their 30's
If they don't have to pay for the car, or aren't faced with the potential of losing it, they'll be stupid.