Pullet and cockerel are correct for the entire first year. After that, hen and rooster/cock. Chick is a subjective term -- use it as you like. Some folks call them chicks until they're grown, some switch to juveniles when they have feathers and come off heat but they don't yet know the sex. Some call them hens and "roos" from the moment they learn the gender. Toss in regional variations and it certainly confuses things.