It does not have to be male and can be any size or age. I would say that using a fully matured bird is going to look better than bringing in a 2 week old chick. No, it does not have to be a purebred for showmanship. But you need to know how to handle the bird in order to show the judge what you know about your bird.
As to how old your chick is, it depends on the breed.
As to how old your chick is, it depends on the breed.