Jerry, Jody is right, they can get picked on. Randy is right too. It just depends I think on the size of the pen. We have enormous areas where the little ones can run away to get away from the bigger ones. When we hatch chickens in the incubator, they stay in a warm house for about 2 weeks and then we put them into another area, by themselves, until they feather out. I would say about a month old. They are still pretty small, but they can outrun the bigger ones and hide, because they are smaller. So, Jerry, my opinion would be, depends on the size of the chicken coop/run. If you wait until they are almost the size of the other birds, that would be at least to the point of about 4 to 5 months old. Have a most wonderful day, a great life. Cindi