I can't say "don't do it" because that would be hypocritical.
I did the same thing at around that age and bought a car with a loan. And spent years wishing I hadn't.
The thing is, it's all very well when you are young, live at home, low outgoings, single, have a decent job.
But, things change and in the course of a year or two, a lot can change.
In my case, 18months after getting the loan/car, I had moved out of my parents house (low outgoings) and down to London (ie lots of money on rent, travel, food, bills, etc), car insurance went up (because of the postcode change) and my job changed too so I wasn't even able to use the car for commuting.
By the time my loan was paid off, I had got married and had my first child
I hadn't thought that much would change.
Seriously, he doesn't know what will happen.
He may not move out in the next 5 years, but he may get a girlfriend (these are expensive on their own), his job may change or he could lose it, the car will probably need some expensive work because it's going to be at least 10 years old with a lot of miles on it.
But it's his life, you can only point it out and be there to help when he needs it.
