He is at peak hormones at his age. It would be better to wait until her pullets are sexually mature before introducing a young hormonally challenged bird into the flock.
This is how I would start and keep as a back up plan. In most instances I can combine such groups after an introduction where chicks can get away from the subadult rooster. You can setup what amounts to a creep feeder chicks can use as a refuge. In my setting the rooster will want subordinate friends once they show he is the boss. They can be later mates.
she would need to keep the rooster separated from the pullets until they matured, and started laying, otherwise he will be trying to force himself on unwilling pullets that aren't ready, a rooster matures on average 2 months ahead of the pullets
