Your rooster is a nut case if he’s mounting 8 week old pullets, or cockerels for that matter. Not sure you need to leave him unattended with the flock if he’s got a “thing” for the youngsters!
Maybe 9 weeks tops. Rooster is blind in one eye and I have a hen that looks similar might have something to do with it. Thought maybe the Roo saw something I didn't. Lol