I used to do this in Australia many years back when I was six and seven. It never even occurred to anyone that it was an issue.
http://www.abc.net.au/news/2017-03-09/how-long-is-too-long-t...
It's certainly a different world now. But I have a 10-year-old, and he goes to the shops around the corner to buy milk and/or bread. There'd be no way I could trust him to make public transport decisions at this stage though. Maybe a year or two more.
What do you see as the relevant differences?