He looks similar to Rhode Island Red.
It’s not so much about size as age. His tail feathers cascading like they do I’d put him at 8 months old give or take.
If your hens hate him you can follow him to roost. He won’t up and leave. He will stay to the outskirts and charm or dominate aggressors one at a time until they are all under his wing. If they free range all the better. He will have plenty of room to evade vs fight.
I think you will be surprised how easy the flock takes to him though. Released one to my flock about that age and they almost all squatted at the sight of him.