Can I say I wish it were more normal? Four is way too young to go unsupervised. We let our son, who is four, play in our backyard (enclosed) while someone is right there watching him out the window once in awhile. If it were a townhome complex, we wouldn't do it. I'd let my daughter play outside in the backyard and pay far less attention (almost 8), but I still wouldn't be too far away.
I sense a time coming soon when my daughter might be able to play in the front yard, too, without too much supervision...but I still think it may be as much as a year out.
I say good on you; keep it up!