This highly depends on the area, at least with schooling. In Indiana, it was around a half mile when I was a child in the 80's. This was where the school wouldn't bus you. Sometimes in high school, it was around a mile. Some folks have to walk a mile and a half.

My sister just spent some time in Connecticut - there were no busses for anyone. Only one of the busy roads had a crossing guard and things for elementary students.

For playing and whatnot, I think this highly depends on area and parents. While I could walk to a friend's house in the same neighborhood in the town I grew up in, my sister often couldn't because the town of 40,000 we lived in was a normal, sprawled, midwestern town and it was often too far to walk. By the time my brother (11 years younger than me) reached some of those ages, they moved to a rural location and distances got further. I had friends with much more freedom than I had, however: My mother was fairly strict.

As a parent, this has not been my experience. In our (pretty affluent and safe) town I still see kids walking to elementary school alone. I let my kids stay home alone when they were 3-5 (you can go with me to the grocery store or play home, your choice) with main fear while I am gone being that of police or juvenile justice Nazis.

The media and government do seem intent on snuffing this out. In their view we must be afraid and any attempt to let kids play by themselves is placing them in unnecessary risk.