tell him to take up skydiving instead. I loved riding my bike, but was always worried about all the other drivers. owning a motorcylce is awesome, but like anything it has its dangers... but skydiving is on a whole other level if its a rush he's looking for. you really can't compare anything to jumping out of a plane imo.
why does he want a bike? to go fast? drag knees? putt around on a harley? pick up bitches??
all of the above, minus the harley?
maybe he's just looking to live a little? bored of the square life wrapped in bubble wrap. no one wants that, waste of time on this earth if thats the way your going to go about it... let him live, if anyting the day he moves out he is going to do it anyway or just do it behind his back. kids always do what they are told not to do.