I have all sorts of aged chickens integrated in a variety of ways, including three 2-week olds who were brooded by their mama hen, eight 5-week olds who were hatched in my incubator, several 3-4 month olds (bought a couple weeks ago), and 15 or so 6-month-old to 2-year-old hens with my 2 roosters. Somehow all of mine get along just fine. I have several coops, but they are all open for the chickens to wander in and out of. I also put my incubated chicks in a see-but-don't-touch coop that shares a rabbit wire fence with some of the older hens and leave them there for a couple weeks before allowing them to wander, but aside from that and the mama hen who protects her own babies, my chickens seem to do just fine together. The littles still have their own coop that they can escape into when they want, but the older hens can get in if they really want, which has never been a problem. It seems to me that as long as you have enough space and food for all the chix, they do just fine together.
I do recommend observing your newly introduced chicks for a while before trusting the older guys with them. But the only problems I have ever had revolve around overly excited young roosters who find my young pullets too interesting. I have been fortunate to be able to rehome those young fellas before they did any damage. My older, more mature rooster takes good care of the bitties. He protects them and their mom. It's beautiful to watch.