There's clearly a difference between not allowing your child to play out at age 8 (reasonable) and not allowing them to play out ever.
I grew up in a village. By around 7 I was allowed to pop to the corner shop on my own.
By 9 or 10 I was allowed to walk to school with a friend, and play out in the woods with friends. We had a den there, and a hidden packet of biscuits that we stored in an old tin. It was a little woods though, just a few houses away so not far, and we wouldn't have strayed beyond that.
From about 11 I was allowed to cycle across the village to my friend's house - a distance of probably 2-3 miles, and we were allowed to take ourselves off to a bigger woods, about a mile away from the house. That had a stream we played in and we built another den, a bigger, better one this time.
Then by 13 I was allowed to cycle the 4 miles to the nearest bus, and get a bus 15 miles to the nearest town on my own. By 14 I was allowed to get a train to a city 50 miles away, again on my own. I also cycled off round the countryside with my friends, easily around a 10 mile radius. Once I was in secondary school, my nearest friend was 7 miles away so I used to cycle there pretty regularly too from 13.
So 8 may be fine, but it's time to start thinking about what you're comfortable with because growing up happens whether you let them or not. Plenty of kids are allowed to play out without getting involved in anything dodgy or causing trouble, though I do understand why you're worried about that.
I would say though that the friends who weren't allowed any freedoms didn't know what to do with all their freedom when they got it all in one go at university. They made a lot of unwise choices then, instead of making small choices regularly from childhood.