I have 5 chicks who are 5 weeks old in the garage with a heat lamp. I have 3 chickens who are 9 weeks old and 2 ducks who are 7 weeks old. What age can I put the younger ones outside with the older ones? I have been letting them see each other with a fence separating them outside and they were raised next to each other in our spare bathroom until we moved the older ones outside.