When I got my bantam Cochin, Carl, I added him to a flock of mixed age hens. He was close to a year old, some of them were 1,2 and 3 yrs. The younger ones liked him immediately, the elder ones bullied him. He was very afraid of them. He was a sweetheart. I think you’ll like yours.
Bantam Cochins, at least in my experience, are mellow tempered birds and will probably be pushed around by older girls. But it could work out for you, do what the above 2 posts suggest, and give it time. Good luck, give us updates…and pics!