Flashy, if its cars etc that your worried about then get in touch with a local motorsport club. even at 14/15 they will get him involved and he will come to respect cars and just how much of a mess they can become if you get things wrong. Its real life crashes rather than playstation ones. Marshalling at rallys etc is a really good way of getting him interested and some types of motorsport can be done before he is old enough to get a road license Autotesting is good fun and dirt cheap. My last autotest car cost £40. They don't even need to be road legal, from a tax/insurance/MOT POV as its all done offroad, you just need a way of getting them there. a favourite is to have a detachable tow hitch on the front of the car, remove the HT leads and it officially becomes a trailer you can tow behind any other road legal car. Education is the key, show him the 'right' way to do it and he is less likey to take silly risks as a form of excitemnet. I also believe that if you show him early on that you trust him enough to let him do stuff like this he will respect you more in the long term.
If its just about not becoming a grannie then I'm afraid its up to you
