I started this year with a couple dozen chickens, a motley crew of heritage breeds. Our (formerly 3) roosters definitely started showing aggression before 6 months. Furthermore, the repeated mounting of the hens is pretty abusive - chicken sex, I'm sorry to say, is pretty much rape.

That said, as you noted, on an industrial scale you would separate the roosters. But it's not clear that there's any market at all for rooster meat. Chicken meat is incredibly cheap and adds surprisingly little margin above the main input cost - feed. Roosters consume just as much feed but produce a lesser quantity of inferior meat. The margins are likely to be negative.

It's an efficiency story yes, but of the "you'll go bankrupt with this idea" sort.