I'm guilty of having done one through five before I was a teen and though I never drove a car until I got my learner's permit, I had a go cart... And man she was fast...
Things I learned from these experiences:
1. Dripping, melting plastic makes a cool noise, and when it touches skin, it sticks, burns and scars.
2. Cut away from yourself, because a sharp knife can cut down to bone.
3. Throwing a spear is fun. Catching a spear is painful.
4. I took apart a lot of broken appliances, and even managed to fix a few. If it isn't broken, don't open it up.
I have a lot of scars from childhood.