I was 7 when I started walking home (only one road to cross, the cul de sac we lived on), a 5 minute walk if I really dawdled...
9 When I had a key and was alone for between 15 and 30 minutes as Mother had to drive to pick my sister up from a different primary school in an entirely different direction, and she had to set off long before I finished to be there in time, as they had a 'collect from classroom' rule.
10 when I was allowed to use an eye-level grill (not eye level for me! had to stand on a stool) to make toast whilst home alone.
11 when I would get a bus to and from school and have keys and be home alone for an hour and a half each evening.
All pre 1992 so no mobile phone to ring mother on. I did have neighbours either side and one a little further away to call on if necessary.
Now - well it depends massively on the child, the route, the level of contact available (can they call the person who is on their way home and talk to them as they make their way home or are they uncontactable til they walk through the door?), the house even...