You are right. While young, first-time buyers are a greater risk for the lender, 22% sounds unbelievably high. He should shop around for rates. He might be able to get a much better rate if you are willing to co-sign.
I would also make sure he understands that whether or not he deals with the same problem throughout his life will depend on whether he lives up to his end of the bargain. Interest is the price you pay for wanting more than you can afford. We're all guilty of it.
The link below will let you look up the usury laws (legal limits for interest rates) for your state.
http://www.usurylaw.com/state/index.php