They are quite old enough to be out free ranging. My only concern would neighbourhood cats and other predators, while they are so young still. So let them out when you have time to watch over them at first. Before you do that, make sure your property is securely fenced in, so they can't escape. Those little things can run fast! LOL Been there, done that...
Then start by letting them out for an hour or 2 at a time. In the afternoon walk over and casually open the gate to their run and stick around to see what they do. Don't be disappointed if they don't come out immediately. Some of the braver ones may venture out at first, but not stray too far. Eventually they will get curious, or see something outside that will attract them. If you spent a lot of time with them and they are tame they may follow you around the yard, especially if you happen to be doing something interesting, like digging over a patch or weeding. Let them get used to the idea over a few days and establish a routine, every afternoon at say 15:00 it's outside time. They will learn quick!
If you have any plants or a garden patch that you don't want them to eat and dig up you will have to fence that off also. Vegetable patches and chickens, for example, do not get along. It took my two broody hens and their chicks exactly one day to completely destroy my spinach patch. I don't know what I was thinking...