I don't do the Cornish crosses. Thye have a limited shelf life so do not fit my goals. They have been developed to put on a lot of meat quiclly and efficiently and then be slaughtered. Unless their feed in greatly restricted, they will develop health problems and die at a very early age. I'll leave the details of that to someone with experience with them.
Not everyone processes their dual purpose chickens at 18 to 22 weeks of age. Some start earlier and some wait longer. The older the chicken, the tougher the meat becomes and the stronger it tastes. Roosters especially. You can fry a 16 week old but don't try that with a 26 week old unless you really enjoy mealtime for you will be at the table a long time chewing that meat. What you have to do is suit the cooking methods to the age of the chicken. The older it is, the longer and slower you need to cook it. We all have different tastes and what I like someone else might not enjoy, but I find roosters even a few years old make great chicken and dumplings. But it has to be cooked long and slowly.
Another aspect of the 18 to 22 weeks is that young chickens gain weight fairly fast, but at a certain age they practically quit adding meat. You pay for feed but get no meat gain out of it. If you are pasturing them, no big deal, but if you are buying feed by the 40 pound bag, it does make a difference.
I raise dual purpose chickens. I try to hatch out a couple of dozen at a time, keep the ones that most suit me for my laying and breeding flock, and eat the runts, the slow growers, the ones that don't have the best configuration, the poorer egg layers, the ones with emotional or behavioral problems, the bullies, basically the ones I don't want to have their genes and characteristics in my flock. I start eating them at about 16 weeks, processing a few at a time. I store the remaining meat on the claw, so to speak, keeping them alive until I am ready for them. I normally finish off the last of that batch around 6 to 7 months of age, by which time I am ready to start on my next batch. At the end of the laying season, when the hens are starting to molt and quit laying, I process the older hens I will not be carrying through the winter. The older rooster is "retired" to that great crock pot inthe kitchen when the annointed crown prince is ready to assume the throne and give me fertile eggs.
This article may be of interest.
Cooking Heritage Chickens
http://www.albc-usa.org/documents/cookingwheritagechicken.pdf
Good luck!!!
