When to free range? Age?

It is never "safe".  If you let them free range, there is always a danger from predators or they may get themselves in trouble, no matter what age they are. 

At what age can they free range.  Any time they are fully feathered out, which should be around 4 to 5 weeks of age.  You can take them out for supervised play time before that, but I would not recommend leaving them on their own before they are fully feathered out.  And they need to know very well where home is so they will return there at night.  Don't move them to a new coop and run, then immediately let them free range.  No telling where they might try to sleep.

Many broodies wean their chicks about four to five weeks of age and leave their chicks on their own, though some keep taking care of their babies for much longer.  But my brooder raised chicks are not raised by and taught how to take care of themselves by a broody.  I generally wait until they are around 8 weeks old before I let mine free range.  Part of that is size.  They are a bit less of a tempting target for a small hawk, but even adults are never safe.  Mostly it is a matter of maturity.  I'm just not comfortable with younger chicks roaming on their own.  Others successfully do it younger than me, but I guess I am just overprotective.

I started before they went to the coop.  They had supervised out time from their brooder when they were just a couple weeks old.  I had to gather them all and put them back, though, and that got increasingly difficult the larger (and faster) they got.  By the time they moved to the coop, I was looking forward to them putting themselves back.  I think it was 3 nights in the coop when I tried letting them put themselves to bed.  And then I asked on here because they were being so very difficult about it.  Well, it turns out they go in willingly for treats somewhere near 7PM so a heaping handful of rolled oats is the price I pay to get them in on my schedule.

And it's always a risk.  My folks recently lost a full-grown hen to an unknown predator (not a feather left behind) right by their house and with a full-grown rooster on guard.  I'm guessing it was an abandoned dog's stolen meal because they live in an area that sees a lot of dump & run pets.

I started letting mine out at 9 weeks. My silkies were a little older, because I didn't raise them, I got them as juveniles (12-14 weeks).

I needed them to at least be big enough that my barn cat would think twice about going after them, since that cat regularly takes baby birds from the nests in the barn and eats them. It worked fine...the cats ignore them.

I agree though that it is never totally 'safe'. My biggest problem is hawkes. I've been letting them out for about 6 months now though, and not lost any. They stay close to the barn. If they're not actively foraging, they actually stay IN the barn. Their coop is one of the horse stalls, which I prop open for the day, but they love to spend hours in the hay storage area. Works well because that is under roof so no hawks.

They go back to the horse stall coop every evening by dusk and I shut the door to lock them in (and the coyotes out) for the night.

Safe or not, I really want my chickens to have a free range lifestyle, at least during the day. They just roost at night so I don't feel bad locking them up in a roomy stall. I guess I would rather have them live free lives and lose one now and then than be captives forever.

Ask me again after I lose one of my favorites, though....I may not be so convinced then....

My girls are the quick out the door -- hardly timid.  I don't think it's a gender thing nor do I think it's age or breed-related because I split a chick order with my mom and her 4 are much, much more cautious than mine (even though they are hatchmates of my chicks).  The difference is that her chicks are being mentored by chickens and mine are being mentored by me.  I think the birds do a better job teaching caution.

ETA:  and I've also noticed that they stay under cover.  They're certainly not stupid   We're lucky enough to have a forest on our property and the coop is in the edge of the forest.  They stay in the brush and under tree cover the whole time.  The most "out" I've seen them is when they were glued to the shed edge and they can get underneath it if needed.  I think I'll need to put some cover inside the run so they'll want to go there.

I free range my chicks all the time! They are about 3 weeks to 14 weeks. Lucky for me I am in a place that has no predators! But I make sure to watch them because you never know what they are gonna eat! Such as bb gun bullets (my dad shoots old cans and such), or a piece of wrapper....Or something weird! lol

I just move my 4 weeks old chicks into the coop today. It is 2-sided and has hinged doors but one side needs a new hinge, so I have them in the side that has a functioning door. I will be making a ramp for them soon (coop is from friend but looks more like a bunny house) and will start opening the door for them in about a month or so.

I want them to at least be large enough to fend for themselves and ward off our Corgi. He's pretty submissive to anything bigger than him but right now they don't really know how to defend themselves against him if he gets a LITTLE too rough with licking and sniffing their butts.

I have six leghorns about three months old and recently got eight more chicks(seven bantams one not to sure) I put the chicks out with the others at only a few weeks old. They picked up doing what the older chickens did and they free ranged with no problems. Just let them free range at first when your doing yard work and see how they do.