My oldest son has just turned 18 and we got him a car for his birthday, also paid insurance for a year and registration. I think that's enough, the upkeep is up to him. He's just finished school and has no idea what he's going to do, I suppose if he decides to continue some sort of study then we'll help out when necessary, but if he gets a job, even part-time, then he should be paying for things himself.
It's hard to know where and when to draw the line, no-one wants to see their kids struggle but they've got to take responsibility at some point.
3b in South Australia.