A dual purpose bird is never going to look like a grocery store chicken, no matter what age or what you feed them. They're just not the same at all. I feed all my birds an all-in-one, not sure the protein % but believe it's similar to Flock Raiser. Plus some corn now and then, and all my kitchen scraps. We just processed two old roosters--18 months and 4 years. They both made decent carcasses. We love dark meat here, and that's where it's at for dual purpose boys. We skinned them, I quartered them and cooked in the pressure cooker 15lbs pressure for about 25minutes. Meat came off the bone easily. Make two big batches of the best tasting soup ever! Yes, the meat had some tooth to it, but nothing worse than roast beef. I don't know who decided chicken shouldn't have to be chewed lol. I have another adult rooster and a bunch of juveniles coming up to butcher, plus a crapton of older hens if no one buys them. I'm just not able to feed non producing birds this winter.