The Model S is the safest car on the road, when used responsibly. And I think that's the key here, especially when talking about a RWD P85+ (yes I know the P85D and above are faster, but the AWD negates a bunch of the "scary" power part of the RWD model), this thing has a ton of power, and if you are not responsible (ie young and inexperienced) it would be too easy to get yourself in a bunch of trouble.
Also keep in mind the other end of the spectrum, you don't need to be using any power to rub against concrete pillars in parkades etc, and the S is a very large sedan making it harder to manoeuvre in those situations than many cars, and has atrociously high repair costs for body work (good luck finding a more expensive car to repair the body work on, or one that takes longer to get the parts needed)
You have to know your child, and nobody here can tell you what is right or wrong for them, I can only say that I personally wouldn't give any inexperienced driver a car as large, as powerful, or as expensive to repair, as a Tesla.
That said, I have to jump on the adoption bandwagon, my parents didn't buy me a car, they didn't even let me drive theirs (even with them present) knowing that, I didn't even bother to get my license until after I moved away from home, there was just no point when I couldn't drive their cars, and couldn't afford one of my own (especially the insurance!)