Our youngest are 1 month old and free ranging BUT We have a large flock, and very small if any of a predator problem. Plus ours stay mixed into the flock pretty well, not much for venturing out into the open. They're coop is right under a HUGE Mesquite tree so they are pretty comfortable staying under it. We still pen em at night, and do hourly head counts of the small ones. 4.5 weeks is still just a little to young. Our rule that we use is if they are small enough to fit through the chain link fencing then they're to small to free range. It works haven't lost one yet. You notice I said yet? You never know. So give em a few more days.