I wouldn't get my kid a Z as a first car either. I'd like to think that I was pretty responsible when I was a teenager but I could only imagine if I had a sports car as my first car. They are just too "provocative". Stupid friends will try to coax you into things, it'll be tempting to drive it faster, to "race", and then there's showing-off for the ladies at school, etc. When the time comes, I see myself getting my kid something slow and boring as a DD. They will find a way to damage the car, no matter what.
On the other hand, father-son projects are awesome and if the kid understands the value of the car by putting his blood and sweat into making it into what it is, then use it to go hit some autocrosses and learn car control. I still don't know if I'd trust a teenager with a sports car, even if they are responsible and mean well. Reasoning and proper critical thinking skills usually don't kick in until at least your 20s.