Mine’s 9 and has been playing out unsupervised since about 5. There’s a small gang who play together and go over the fields together. They all look out for each other (although the eldest of them is approaching his teenage years and has decided to be mean to my daughter, so she just comes in when that happens)
Contrast this to a friend of mine who wouldn’t allow her children to play unsupervised in their own garden until the eldest was 9!! Crackers!!