I find when they are about 10 to 12 weeks of age is a good time to introduce.
It's good that the girls are older, and can haze him a bit, as it will help him learn manners with his hens. However, still watch as he matures. One of the least successful pairings is same or close age young roosters raised with siblings to form a new flock. Often the males become quite aggressive with the young pullets as hormones kick in, and the girls are not mature enough to know what to do.
The best pairing is a young teen placed with mature hens in an established flock. He has to learn to woo them in order to get any attention or they kick his tail feathers.
The trick is to have the rooster old enough to withstand reasonable hazing but young enough to learn from it.
So when he is 12 weeks of age, the hens will be mature and laying with a stable flock structure. It is unlikely they'll put up with too much nonsense and he'll have to convince them of his affections.
If it is too rough, pull him back out and retry at 16 weeks to get the right balance of being put in his place without over hazing.
Continue to watch dynamics. Manipulating flock dynamics can influence outcomes, but nothing will replace good genetics of temperament. If he is not a nice roo, do not allow him to terrorize the hens. I find those males best with dumplings.
My thoughts. Good luck

LofMc