How old should pullets be before out with a young but mature rooster?

the rooster ( George) is mature but very young and has not had any ladies since I found him outside, he's been through a months long quarantine process as I couldn't put him with my existing flock as they already have a rooster and there are only 5 hens. I'm growing these isa brown girls for him and they are 5 weeks old ( give or take a day, they are about a fourth of his size and fully feathered). my question is how much more time should I wait to introduce them? they have been separated in an xl dog crate for about a week in his coop. He hasn't shown any aggression through the bars and eats with them despite having his own food 24/7.