My test if it has aged enough for rigor to pass is that the joints move easily. The meat needs to be flexible, if it is stiff at all then it is not ready. You see suggestions for 1 day, 3 days, or 5 days. That is because not every bird reacts the same. The age of the bird, temperatures and other things I don't know about can give different results. Go by what you see, not hard and fast rules.
I don't go by hard and fast rules about ages either. Cockerels mature at different rates. How we keep them can have an effect on how we can cook them. A big factor to me is your personal preferences. The older they get the more flavor and texture they get. Some hit puberty earlier than others, the hormones of puberty speed up flavor and texture development. If you are used to store bought chicken it will be different. Some of us like those differences, some don't. Don't be surprised if what you experience doesn't follow any chart exactly. You need to be a little flexible.
Still, age is all we have to go by. How old will they be when you butcher them? Depending on their age there are a lot of different ways you can cook them. Coq au Vin is a way to turn an old old rooster into a gourmet meal. That is a form of stew. Soup can work but never let it hard boil, just simmer. I bake a lot. You can use them to make broth and pick the meat for chicken salad, tacos, or soup, but use a long slow method. I use a crock pot on low for about 24 hours and often use that meat for sandwiches for lunch. You can pressure cook it and get really tender meat. If you pressure can it in accordance with a tested recipe the meat will be fall off the bone tender.
Whatever cooking method you decide try one and see how you like it. If it works for you, great. If not, try something else.
