They eat a lot & they mature very slowly. The males don't really finish out untill they are well over a year old & the females are late layers. They are also amazing looking birds & you'll hear a lot of "I didn't know chickens got that big".
All this assumes you buy quality stock. I've seen some hatchery "Giants" that were smaller than Australorps. They only place I know of that sells chicks that are from well bred birds is Sandhill Preservation Center.
I have only one white left, and she's been a reliable layer. I don't know where she was bought from, since I got her as a pullet, but she's a huge girl. They do mature slowly, the males not fully mature until about 18 mos. My girls didn't start laying until they were about 9 months old.
Um, yes. Yes they are! If you went and looked at our pics you are seeing babys! Even at 7 months old they are bigger than our fully grown large fowl buff orpingtons. Our BJG roo is twice their size at only 7 months. I wasn't trying to shoot down your "facts" I am only saying that I am proud of our birds developement this far and their early laying.