look at their combs. Cockerels will be really red quite young. Pullets redden just before they start laying. Also Cockerels tend to be more aggressive towards other chicks.How old does a chicken need to be before you can tell if its a rooster or a hen? And how can you tell? I have one that acts nothing like the others not flighty at all jumps onto my hand and lets me feed it while the others fuss over the feed that hits the ground. Im guessing they're about three weeks old I got them from tractor supply were all supposed to be pullets. Either White Leghorns or something else not sure they just got all their feathers in they are all white.