I actually think 'playing out' is overrated. Fair enough if it's a child playing proper games with one or two close friends then that's lovely. I used to do that when I was little. But just going out and playing with whoever is out there, often much older kids is not great in my opinion. My nephew has 'played out' from the age if 5. At first it was just his street, then in about 3 local streets. It wasn't the cars that was a problem, it was the fact that this gang of little lads could not play together without it ending in tears. I used to hate babysitting in the summer because his mum would say he was allowed out so I had to let him, and inevitably he would come back crying about something another child did, or he would come rushing back followed a few minutes later by a couple of other kids complaining about something he had done. They never seemed to play proper games, which was part of the problem, plus weren't really good friends, just happened to live near each other.
Another boy I knew, aged 5, was in the class I taught. I used to walk home every night past his house and he would always be playing outside with a group of children, and a few were quite a lot older than him. He was very good at manipulating other children and getting them into trouble, in a way that is unusual for a child so young. I am sure it was because he was always around older, streetwise, not very nice kids.
Also, where I used to live there were a group of children that used to play out a lot. Their games used to involve lots of chasing, often through the front gardens of other residents who didn't even have children. They also seemed to gang up on one or two children within the group. My next door neighbour, aged about 9, who I think had a learning disability often seemed to be the victim, though would always play with them again as I think he was just desperate to be included in the gang. From the things I heard them saying to each other they didn't seem very nice children and I wouldn't have let my child play with them.
I can remember being about 9 and being desperate for kids in the street, who I wasn't even friends with to call for me so I could 'play out.' My mum told me it probably wouldn't be as much fun as I thought and she was right. One day 2 girls in the year above me at school called for me and we rode to the park behind our houses on my bike. We then just sat on our bikes there for a while, they didn't really talk to me, then they rode off and left me, so I went back home. After that I was happy to just ride my bike in the street with my best friend or play at her house or mine.