I've got a flock of 3 hens and 1 rooster that are 14 months old. One hen hatched a few, but had no interest in brooding them so I took them. They are 8 weeks old. I also have 6 littler ones, about 6 weeks old.
The 8 and 6 weeks were together til they outgrew the brooder, at which point the would all go outdoors in a pen together during the day, but slept separately. Several days ago I put the 8 weekers in a dog crate in the big chickens' coop. They stayed in there for a day and a night, then they got to go from their crate through the pophole into a temporary fenced area outside. The big chickens were happy going out the people door that I propped open. We picked the beginning of a three day weekend for us to try this so we could supervise.
After two days, I took the fence down and moved the crate. Now everyone has access to the crate and the entire coop and our 75 acres if they wish. The hens are quite disciplinarian with the 8 week olds, telling them where they can and can't be, that they can't eat until the big chickens are bored and go away, and generally being clear that little chickens are nowhere in the pecking order.
They are essentially two separate flocks as the little ones quickly learned to leave the big chickens alone. Interestingly, the rooster is being pleasant to everyone - a surprise as I'm nearly certain I've got two roos and one pullet in the 8 week old group. I am worried about the young ones as they seem to think they have found chicken Utopia and are happily running around, expanding their horizons every day with no thought to danger. The big chickens are aware of hawks and other predators, but the little ones don't even know to look up yet. We'll see if they integrate more and the little ones learn from the older ones. I hope so! Today was their second day of total freedom and they were as far as 400 feet from the house and coop already.
All free ranging chickens spend a considerable amount of time each day gossiping outside the pen where the 6 week olds spend the day.
I have no idea right now how I will safely integrate the 6 little ones in a couple of weeks, unless the current three do really become part of the flock by then. Right now it looks as though they will stay separate. I have already explained to them that the coop is big enough for all, although barely, and I am NOT building anyone another one. Hopefully they are listening.