how do i tell the chickies gender?

[:D chicken]

well the older chickies, since i am pretty sure some are older than others, have bigger combs but their feathers are also more developed too, and generally sparky and dottie and lizzie who are my big ones have bigger combs but i thought that must be normal and i dont want to have to get rid of any of them so u kno do u think they might also just be older?