Would you want your kid to start taking flying lessons in a Cessna, or a Gulfstream? That car is way too much for him, IMO. It'd be like going skiing for the first time and deciding to take your kid up to Jackson Hole and have him jump off the ledge into Corbet's Couloir. I think you are setting your kid up for disaster.
This may be beyond the scope of your question, but why not tell your kid he can get the M3 once he has enough money saved from his JOB to pay for it. My father wouldn't buy me a car, or pay for gas/insurance/repairs, etc. The reason wasn't money, as we were pretty well off, rather it was to teach me responsibility. While I wasn't happy about it then, I thank him for it now. And it made me appreciate my 1972 Chevy Impala that much more!! I don't think your kid will appreciate the M3. It will make him feel entitled though.
Congrats on the good grades and not smoking. Sounds like a responsible kid. Why endanger those responsible habits by giving him such a high powered car?