The only person allowed to drive my car or truck is my wife. My kids may be able to drive my truck when they're old enough. I don't share my toys as I paid for them and have to fix them. I also don't share my wife as she is my toy to play with.I don't have specific or "hard and fast" rules.
I do have a few caveats:
1. If you spun wrenches on it you can drive it.
2. If I trust you, you can drive it; and
3. If you had my children and fund my habit you can drive it.
My biggest concern is with people who lack understanding or mechanical sympathy for things that are not simply appliances.
I let my brother in law drive the Kitty a few weeks ago. It was far and away the most powerful thing he'd ever been in or driven. But, I was there and he was responsible.
It's just a car... and not sharing your toys makes you a bit of a d*ck.