Personally, I think you are crazy for buying a teenage son their own bike!
I was one once and thought I was invincible at 17. Then again, maybe I'm just jealous since I had to buy my own and my mom wouldn't let me do it until I was 18. Didn't have much money so I bought a little honda. Had it for a about a year until I realized that I wanted a harley. 15 years later, I finally just bought my hog.
Bought a Street Bob two weeks ago and LOVE IT. I haven't had a bike in years and have no problem riding this bike. Probably a good one for him to start on. If he tall, you might want to think about the forward controls though. I'm 6' 3" and wouldn't be confortable on this bike without them.
p.s. MAKE HIM WEAR HIS HELMET and take a riding safety class!! Even exerienced riders say they benefit from the class.