A 6 month old female bird is called a pullet, not a chick.
Actually, I call all the female chicks pullets as soon as I know they are females.
I guess you could call them all chicks until they stop peeping...or lose their down.
FYI.....semantics, maybe, but can be important communication terms when discussing chicken behavior.
Female chickens are called pullets until one year of age, then they are called hens.
Male chickens are called cockerels until one year of age, then they are called cocks(or cockbirds or roosters).
Age in weeks or months is always a good thing to note.