I agree with mama bri, it's definitely up to the parents. I have 3 boys aged 13, 11, and 7. I can leave the older 2 home to run to the store. But my 7 year old is a wild child and I don't leave my oldest children with that responsibility yet. You have to be comfortable, so follow your gut!!
I leave them all with my oldest, but they don't bother each other. It is just a body in the house they each do their own thing and are self efficient even my 8 year old. It's just idk. He's still a kid I feel like.
I think its really up too the parents what they feel is ready if there child is mature enough too be home for little bit of time