I think I agree with you there. Being a small petite female (or just a female in general) I'm also at risk from a man who wants to do me harm so there comes a point where age makes no difference in that respect.
With age comes maturity so what to do if someone approaches you/tries to drag you off the street/how to cross the road.
Independence is so important and I do think a lot of us (definitely me included!) are guilty of not allowing that because we fear the consequences.
So whilst 8 is maybe a little young for doing the suggested, start smaller and build up.
My 9 year old is technically allowed to walk home but I don't trust him. So I've decided as of today instead of meeting me in the playground he can meet me outside of the school gates and wait for me there. It may as well be in the school playground with being how close it is but I won't be there, I need to trust he will wait for me. We've had almost 2 years of him leaving his classroom alone and finding me in a different playground so we are just building from there.
Once he's proved himself capable and trustworthy he can meet me further away gradually until he starts year 6 in September and then he can walk home. I won't be far behind him anyway so I can likely keep an eye on him.
Then in a few years I'll be doing it all again with his brother!
It's so much easier when they are babies and you can't let them out of your sight!!