It honestly depends on the lines. Some lines of Wyandotte aren't finished filling out until 18 months. Some even longer. And production strains, hatchery stock, can be completely finished in 6 months.
Feathering in the hatchery stock is usually finished by the 6th month, at least they were when I had them. The birds bred for standard generally don't feather out fully until 9 months of age, and aren't filled out until about 12 months. But again, it's just a generalization.
(Conformation not confirmation. Confirmation is saying you confirm something to be correct. Conformation deals with the body type of an animal.)
Feathering in the hatchery stock is usually finished by the 6th month, at least they were when I had them. The birds bred for standard generally don't feather out fully until 9 months of age, and aren't filled out until about 12 months. But again, it's just a generalization.
(Conformation not confirmation. Confirmation is saying you confirm something to be correct. Conformation deals with the body type of an animal.)