If they've been in their current coop/run for quite some time, IMO they're old enough now. It'll probably be suggested that you wait until they're laying to be sure they know to lay in the nest boxes. My girls never had any issues heading back to the coop to lay, but some folks have had issues with their birds hiding nests/eggs out and about. You could start letting them out only in the evenings...maybe 5 or 6ish. That way they learn to head back to the coop as it darkens, and it's past prime egg laying time. Maybe do that for another month or so until they're all laying???? But at 4 1/2 months, I think their size is big enough for ranging without being a super easy target...