Between 8-10. And you have taught them how to advod strangers and the dangers of cars. Especially that if you don't live in a walkable city. I taught my kids that lot of people in the cemetery who had the right away.

One of the biggest rules that I established first. Always give the car the right away. It sucks, but when you live in America were they are car obsess you have no choice. Beyond that kids should be free to roam and play outside without parents hovering.

Now also note may want to check with your local city or state,because some actually have laws against it. Like fucking Florida.

In Oklahoma kid can stay home alone at the age of 10.