It’s never a good idea to buy an 18yr old a brand new car, in my opinion. Let them cut their teeth on a mechanically sound beater Corolla or Civic first, and then after they’ve had their share of accidents and become a better driver, sure it may be wise to buy brand new. 

But as a first car, buy a cheap beater car, with cash. That way, if they wreck it, you don’t care. It surely won’t make you regret it compared to wrecking a brand new car. 

Buying a first car is tough when you have no credit. If you can get financing, you're going to be paying a high interest rate and probably dealing with a shady car lot that does in-house financing. 

Alternatively, you could co-sign with him to get a good rate on your credit. That would help him get established without overpaying for the car. 

Just depends on what your relationship is like.

No, and there are many reasons for it. I would get a 2-4 year old car. There are many good options depending on your needs and getting a new car is a waste. 

Young people will get tired with brand new car before it worn out.

So, 

In my opinion that would depend is someone willing to cosign does he have a stable job does he plan on working at that job for the length of the road how does he drive is he likely going to crash it and you cant forget about the insurence and the regestration being threw the roof.

Building credit is a young man's bullsnot line.  Credit can be built on a old beater if that is part of the deal.  Instead of paying cash, finance, and consider the finance charge charges for a credit rating like the rest of us buying on time.

Then after their income increases they can buy new with their own money.  Live and learn.