Ok, not to horrify anyone, but with the cornish chickens (not the cornish rock hybrid) and heavy breeds (like orpingtons)I've read that butchering age is usually around 13 weeks. I was wondering if by this time the cocks would be tough or still nice and tender. Sorry if I offended anyone. Thanks!

No problem. Traditionally with farm flocks in the US, the goal was to dress out the cockerels at about 12 weeks. This is what my grandparents did (and I did a few times, too) in the 1950s and early 60s. These chickens made fryer-size dressed birds, weighing around 2 pounds or a little more, and were reasonably tender. Of course, we were not spoiled then by the Cornish X roasters that are everywhere now. My memory of fried chicken in those days was that it was very good, a little on the small side compared to today, and not as tender as we have come to like now. Of course, everything my grandmother made was wonderful.
If you went to sixteen weeks or more, I think you would begin to see toughening in the birds. Even then, they make good soup. I recently tried making soup out of a two-year-old rooster. The broth was okay, but we could not cut the meat. Good luck.