How many girls and how old are they?
Sounds like pretty normal behavior for a teenage cockerel especially if he doesn't have any older hens or a older rooster to teach him some manners.
If he's with same age pullets, he's learning all this on his own. Cockerels mature much faster than pullets, he's wanting to mate and the pullets don't know what's going on until they get close to point of lay.
If you see he him getting too overly aggressive you could separate him from them until they all are laying. Another option is only letting him free range with them during his non peak mate times (morning and night).