A nordic capital, 1mil population, old-style city centre. https://commons.wikimedia.org/wiki/File:Stadsplanesystem.jpg https://commons.wikimedia.org/wiki/File:S

A nordic capital, 1mil population, old-style city centre. https://commons.wikimedia.org/wiki/File:Stadsplanesystem.jpg https://commons.wikimedia.org/wiki/File:Stadsplanesystem.jpg (1st picture). 15 minutes walk to central railway station connecting (kind of) to the rest of the world. I'd say the independent/free play-area radius extends beyond the inside yard sometime between 4 and 5, by 10 kids would be cycling all over the city by themselves. Most would walk 10-15 mins to their kindergardens themselves (?) from about the age of 5. I wouldn't consider this an outlier, and my family wasn't particularly laissez-faire. Many friends would go cycle-touring or interrailing in Europe between 15 and 20. Doing a solo interrail in Europe for a month is a culturally established "rite-of-passage", although people will usually wait till they turn 18 to go alone.