As an animal ages, the meat changes texture and has more flavor. Veal comes from a young calf, probably still mostly drinking mother’s milk. A baby beef is older and has more flavor as well as texture. An old mature bull is strong and tough.
Chickens do the same thing. The older they get the more flavor and texture the meat has. This is more evident in males than females. But that does not mean the meat from an old bird has to be tough. It all depends on how you cook it. Coq au Vin is a traditional French method of cooking an old rooster. That meat is quite tender and delicious. The secret to cooking an older bird is to cook it slowly and with moisture. The older the bid the slower you cook it and always with moisture. So why was the meat tough on yours? Mainly the way you cooked it.
When do you butcher a cockerel? Different people use different ages. If you get them pretty young you can still cook them like the ones you buy at the grocers but there is not much meat there. If you wait until they are older they have a lot more meat but you have to alter your cooking methods to keep it tender. The commercial chickens you get at the store are butchered at 6 to 8 weeks. They are still very tender and don’t have much texture or flavor.
I normally butcher cockerels about 18 to 22 weeks old, though sometimes I go a month or more than that. When I cook them, I coat them in basil, oregano, and sometimes a little parsley, then put them in a baking dish with a couple of tablespoons of water. The baking dish is sealed so none of the moisture escapes. I normally bake them at 250 degrees Fahrenheit for about 3 hours, but the older ones may be cooked for 3-1/2 hours. I’ve cooked very old hens and roosters using this method but setting the over on 240 and cooking them for an extra hour or so.