Girls can act boyish, especially if they are a dominant bird (or trying to be). I had two cochin bantams I was convinced were boys because of their behaviour as chicks. One is very dominant and keeps the older chicks in check! But they turned out to be girls. We also have an Old English Game bantam hen who will mount our Wyandotte bantams as a show of dominance. I'd expect some comb and wattles by now if your bird was a cockerel.