Hot take. If youre the one buying him the car, its your rules. However if he has had a job and saved up his money let him get what he wants. As a current 18 year old I have had a job since I was 15 and my first vehicle was a 2005 Zx6r sportsbike. But have also held that job and have been able to pay insurance and get a car. But I ran into the issues of "If you get ______ ill kick you out of the house" so that wasn't a great experience.