I tossed 2 of my older hens in with my 8 week and 5 week old chicks. They did fine. I'd already have integrated them by now, but am waiting for help to move the electronet fencing so it encircles both coops. As long as your flock has PLENTY of room, integration with younger chicks usually works pretty well. I've done it at 6 - 9 weeks without incident.
