Usually guess work. Or what the people decide or the way of life calls for. It seems like places where there isn't as much easy public transportation can have lower ages for when you can get your license. Usually if people over the age aren't responsible, they'll end up doing something that'll cause them to lose their license, but it isn't always that fair. And I wouldn't say that means your father isn't responsible. It just means he hasn't learned what he needs to in order to get his license. He could probably learn if he wanted to, but not everyone feels the need to.
Same with my world really. If a fight comes up, you do what you need to. Practice does help to make sure you get out of the fight ok though.