This is my 13 week old Old English Game bantam cockerel. You can see how narrow and pointed his hackle and saddle feathers are (not to mention those beautiful green tail feathers which I love). If you look under the feathers at the base of your bird's tail you might see skinny, pointed feathers coming through if it is a cockerel.
View attachment 2268941
A lot depends on how fast or slow certain lines of birds mature. I was only able to keep our Pekin hens as we were in the city and at 10 weeks they all started sprouting their wattles and combs. And our mottled girl was red in the comb from a very early age, so much so that I sent her back to the breeder with the other cockerels. The breeder wasn't convinced and a couple of weeks later returned her as she was positive she was a pullet.