For those that do let them out, at what age do you feel comfortable doing so?
Whenever you want to start feeding the wild life. You got those predators in the area, you are going to be feeding them. And often times dogs can be predators too.
I hate to rain on your parade, I love to free range mine, I have had better luck with a year old rooster in my flock, but I have lost a lot of birds due to predators. Once the raccoon left a note, "Please leave BBQ sauce, I am tired of them plain." And just this fall, I butchered the first roo, and while I was catching the second rooster to butcher, something took my the first one. My flock has been in lock up since December..... I have let them out and about a couple of times lately. As when the predators don't get a free and easy meal, they move on.
My girls on the top of a creek, lots of cover, and until I had a year old rooster, I lost something 2-3 times a month. When I got an adult rooster, it did help, till something got him. I do have a dog that does not bother chickens which is what I have, I think they get used to her, and are not as wary to fox and coyotes.
I love to free range them, and I do weigh it with the risk. But I have a predator proof run, and I do use it.
Mrs K