Just out of curiosity, where did you get them? Not that it’s that important to your question but hatcheries don’t generally sell true Ameraucanas, instead they sell Easter Eggers so you really can’t go by the standard Ameraucana size for adults. Some hatcheries give expected weights of adults with their ads for the birds so maybe you can get some help there.
Technically a male chicken under a year old is a cockerel, over a year old they are considered roosters. Different cockerels put on meat at different rates too, even the same breeds from the same flocks. So while I’ll talk about ages understand there could be a lot of differences in your individual birds.
You can eat any chicken regardless of size or sex. People eat quail so obviously you can eat a small chicken. But there are a few things to consider. When they grow they first build a skeleton, then add meat to it. If you butcher them pretty young you just don’t get much meat. The other is that you have to adjust your cooking methods based on age. A very young chicken is tender enough to fry or grill. But the older they get the more you need to use slower moister cooking methods. Coq au Vin is a French recipe that turns a very old rooster into a gourmet meal. Different people have different expectations too. If all you are used to is fried or grilled chicken cooked from the chicken you buy at the store, you might not like the taste or texture of older chickens. The older they get the more texture they can have and the flavor changes. The changing texture is why you have to adjust your cooking methods.
Most people are OK with frying or grilling a 12 week old cockerel but there just isn’t much meat there. Some people can handle a 15 o 16 week old cockerel fried or grilled but some people would consider that too tough. I think some of that is how you cook them too. If you fry them in a lot of lard at a really hot temperature where you leave the lid on the pan they may be preferable to one fried in a little vegetable oil. I think technique plays into it too.
Generally I don’t butcher a cockerel until he is at least 16 weeks old and I actually prefer them after five months. By 16 weeks most have put on a reasonable amount of meat though some can still be pretty small. For the next 6 to 7 weeks they normally pack on weight pretty fast, have a growth spurt. But them they greatly slow down the rate that they grow. They’ll actually keep growing for over a year but that rate gets to be pretty slow.
There are all kinds of ways you can cook older birds: cock pot, pressure cooker, stews, chicken and dumplings, for some examples. I generally cut a 23 week old cockerel into serving pieces, rinse those but do not shake off the excess water, coat them with herbs like oregano and basil, then bake them in a tightly sealed baking dish for about 2-1/2 to 3 hours at 250 degrees. I’ll do an old rooster the same but cook at 240 degrees for at least four hours.
I save the bones from what I eat and add them to the back, neck, and other parts I don’t serve at the table and cook them covered in water in a large crock pot overnight, usually 14 to 15 hours. I add a bay leaf, a dozen peppercorns, a chopped carrot, onion, and celery, some garlic and some herbs. When it’s done I strain out the liquid and remove the fat. That’s the best broth you’ll ever taste. I also pick the meat out of the stuff I strain off being careful because there are some small bones and use that in tacos, casseroles, soups, any way you might use cooked meat.
I don’t know the “best” age for you to butcher or for your cooking method, it’s all so personal. But if you really want to eat those cockerels you can.
