At what age are chickens considered full grown? I don't mean so much plumpness, but height wise. I've never had bantam chickens before and they are 6 weeks old now and I want to permanently install feeders. but not sure what their adult back height will be. Will they get much taller? (I've never had bantams before, so I have absolutly no clue how big they really get ) These are bantam welsummers. Thanks!