Speed of maturity depends to a great extent on how the birds are raised, as well as genetic factors. You should have no trouble determining males from females by the age of 12 weeks if they receive good care. They also mature more quickly if they have access to the outdoors or grassy runs.
Generally, the males combs will be larger and redder, and the hackle and saddle feathers should be pointed, whereas pullet hackles and feathers in the cushion area at the base of the tail should be rounded. If you need more help, try to post some photos. To answer your other quesion, hens and pullets will spar with each other, and with cockerels until a pecking order is established.