I just asked DH and he replied with 40

It would depend on circumstances for me. The neighborhood you live in, for example. At the moment, we live near a super busy road, with no crossing or pedestrian lights. So that would make me really uncomfortable with letting DD go on her own during primary school years.

I was only ever allowed to catch the school bus (specifically for our school) and walk home from the bus stop once I hit high school. I wasn't allowed to stay home alone when we lived in the burbs but we moved to acreage when I was 12 and we were allowed to stay home during the day alone there, provided the lady on the next property was home. I was a lot older before we were allowed to stay at night. I guess it's knowing when your kids are ready and responsible rather than an age ITMS.