Interesting. I change my dual purpose chicks over to grower (16% I think) at 8 weeks and notice a big growth spurt. Don't know why, don't care why. Could be cause that's when they can start wandering about the yard, too.
I process when they start crowing to much and become irritating. Once I have decided who is going they do and I process a few at a time. I don't mind having a small Roo per person or for 2 people. Usually I start processing at 14 weeks and am done deciding by the time they are 17-18 weeks old, but not always. That way their meat is still mild flavored and tender too.
Mature Roos are not that tasty. No matter how long you cook them. If you do process mature older Roos, soak them in buttermilk to take some of the wildness from the flavor and it does tenderize them also.