The meat becomes tougher as the birds get older and the muscles develop. It has nothing to do with hormones, it will happen with both hens and roosters. Dual purpose breeds such as your barred rocks will usually be somewhat tough, even at 16 weeks or so. Any bird I've butchered past 12 weeks old has been at least a little tough. Yours are already past being fryers, but they can still make really tasty meals.
But if you cook them right, they'll get tender. Many French recipes, such as Coq Au Vin, are traditionally made with older roosters, because they have more flavor than young ones.
Breast will remain tender even in an older bird, you can debone the breast and fry it, and the thighs, to a lesser degree. Because of the exercise they get, they'll be a bit chewier than the breasts. Put the rest in a crock pot, and it will get tender after several hours. You can also cook it in buttermilk, that'll make it get tender faster. Marinating in buttermilk, or pineapple juice, or yogurt, or any number of highly acidic marinades will tenderize the meat. Or cut up the whole bird and cook in the crock pot.
I cooked one a few days ago, that turned out especially tasty. He was a 20 week old Delaware. I cut it up, put it in the crock pot, seasoned it, and added enough buttermilk to not quite cover it. After about an hour and a half, I turn the peices so the upper parts were submerged. After about 3 hours, it was fairly tender. Without buttermilk, it may take closer to 6 hours to become tender. I took it the crock out of the base of the crock pot, and put it in the oven to finish, so it would brown a bit. Next time I'll transfer it to a baking dish, so more of the parts will brown. Anyway, it came out tender, moist, and really yummy. My DH loved it.
Buttermilk will separate and curdle when it's heated, but the curds just get brown and tasty, the whey makes the bird tender.
