As a parent I asked myself what was the worst thing that could happen to my child if they did "X". If they wanted to walk on a wall 2 feet off the ground they may get a skinned knee. Ok, good learning experience. What could happen if they wanted to walk on a rooftop? Hmmm, broken neck. Better not let them do that.
Different ages allow different experiences. If you are thinking of what's best for child you never will go wrong. Reminds me of a parent asking me why did I allow my son to own 22lr and 410 at 6 years of age. They said it was dangerous. I said if a child only sees a gun on a video game then they think shooting someone is no big deal because they just shrug it off and keep going. However if they see that if you pull the trigger and take a life, be it a bird or a squirrel, death is permanent. Life is a learning experience and it's up to a responsible parent to teach their children. Different methods for different folks.