I've driven other peoples cars, and I've let my brother drive mine. I wouldn't have a problem loaning the car out to certain people, obviously there needs to be a level of trust there. As stated, if something does break, or the car gets wrecked, I wouldn't expect payment, just as easily could happen with me in the seat.

I agree with the others, now might be a good time to slow the car down a bunch and let your grandson take it for a pass. I'd never been faster than 15.0's at 80 mph when my dad tossed me the keys to his 70 challenger. First pass was 13.0@110 walking into it, the second was 12.47@111 getting on it a little quicker. Been hooked since.