Used to roam up to a mile at age 7. Back before dark was the only requirement.
If I look back, I’d roam up to a mile easily at the age of 3 or 4. That was with an older brother and sister though. Not on my own. Spent a lot of time with my sister and she was 3 years older than me.
By the age of 7 we were literally wandering miles, to the point were we occasionally got lost and had to ask for directions to get home. That said, we weren’t meant to be doing that…
It was just what you did though, and I don’t see why it should be much different now. I wouldn’t be worrying much about people driving around and trying to pick up kids, there are probably a billion bigger risks than that. I wouldn’t feel comfortable with kids playing near a busy road for a start. So depends very much on the area, but a little adventure is good for them.
To be honest, while I can appreciate the concern, it amazes me that many parents don’t let their kids out of sight.