well...we just started that when my son was 11 but we live near the main busy street on a military base...even I have to be careful with crossing the street when walking our dog.

My kids are 5, 6 and 8.  We live on a dead end street with only 7 houses and I'm still not completely comfortable with letting my kids play outside alone.  I've let my oldest 2 go out of our driveway on ocassion for short periods of time with the neighbor kids who are the same age as my oldest 2.  They let their kids roam but they carry a two way radio, stick together and clearly follow their family's rules.  I sort of wish I was more comfortable with my kids doing the same but I just can't!

Ugh. Never? People drive like idiots in this neighborhood, even though we live on a cul-de-sac. We often sit outside while the kiddos play and we aren't watching their every move. That's as close as we get right now.

I think mine were about 10 when I felt sort of comfortable. It is nerve-wracking. We are in a nice neighborhood, but still we are only 7 miles from downtown Seattle and we are close to a bus route. You just never know who is wandering around.

We live out in the country and on a private lake. The kids mainly just play in our yard. We do have another house on the lake 4 houses down from ours. Sometimes if I am swimming with them at that house and my older son who just turned 8 forgot his Kindle at our house, I will allow him to walk back to our house to get it. That only started very recently. They can ride their bikes up and down in front of both houses where I can see them but not around the lake by themselves. My kids are very cautions. 

Depending where we live. Cities I was definitely more protective, smaller towns I let them out around 8, they weren't allowed after dark until around 12.