However, different children reach this at different times.
For example,
At 8 my daughter was allowed out to the park. Our rule was she could talk to people, but must always check with me before she goes anywhere. Once, whilst playing at the park, she saw another girl from her class whose mum asked her to go back and play at their house. DD replied she wasn't allowed anywhere without checking, borrowed a mobile phone and phoned me to ask. I said yes, and she happily went to the friends' house.
Another time, she was playing at the park and the friends she was with went to an area that was out of bounds. So DD came home and I gave her a treat for making the right decision.
I have hundreds of other examples like this. Another mum has even stopped me to say that she has seen DD playing at the park and has been impressed that DD was quite forthright with other children by saying "I'm not allowed to play there" or "I need to check with my mum first".
But, we give her a significant amount of freedom on the understanding that if she breaks it, she loses it. Full stop. Whilst I allow a lot of freedom, and am laid back in many ways, I am very strict about them breaking rules. So given her personality + her fear of losing her freedom, we've never had s problem with her breaking rules - even when other children have. This has been reported back to my by other mums at the school gates, as well as by my daughter herself.
But then, we spent a long time building up to it and preparing her for her freedom, so by the time she was allowed to go to the park, she was well prepared for dealing with it. I also spoke to my social worker friend, who gave us lots of different ideas about keeping her safe.
The point I'm trying to make is that for as many examples as you can give of children going astray and not obeying the rules, there are just as many examples of children who are sensible and do follow the rules, and those who can handle the responsibility at an earlier age.
I also think every child and every situation is different. For example, where I live, lots of children still play out - so there are a lot of mums constantly popping over the park to check the children are okay, and as the overwhelming majority of children go to the village school - most children know each other, and most parents know the children too. So if I were to see something untoward, I would say something to the child / parent as relevant. It works where I live, but when I lived in a large town, I would never have given my children the amount of freedom they have here, because the situation was different.
I think it is very difficult to stand in judgement of other mums over the Internet, because we judge on the basis of our own situations, and no one ever really knows what another person's situation really is.