In my copy of the SOP there are some definitions which may help:
Cock - a male fowl one year old or more
Cockerel - a male less than one year old
Hen - any domestic female fowl one year old or more.
Pullet - a female less than one year old
Someplace, I thought the discussion weighed in that the pullet probably should be POL or older so most likely you would want a pullet to be between 6-months and 1-year old for a show. HTH
X2 I've been told that if the pullet is not laying yet she will receive an "age" markdown.