I would probably start eating them at 3 months and the last one I would eat before a year, maybe as late as 10 months. But I like butchering one at a time, aging it in the fridge for two days and then cooking. I like to skip the freezing the meat part.
The first one that I ate would be the one that started to be a bother first.
Truly though, that is how I do it.
Some roosters start to be all full of themselves sooner than others. I would hate to guess an exact age though.
But eating whoever is being a pain makes the butchering more fun. I still remember one rooster we ate when the kids were still little. The rooster had started puffin up and trying to attack the kids, which was why we ate him. He was a little old, so we made him into an enchilada casserole. The kids would take their forks and stab it into the casserole and say things like "That is what happens when you give me owies! Hahahaha!" and "nasty rooster tastes GOOD!" It was great fun!