Mine grew huge fast too. And developed really early on. I had heard that chickens don't lay until six months old but mine started at four :O this is my big ol' roo
Really? I knew he was big but is he abnormally so? He gets layer mix at the moment because I have that for my hen. Is that ok? I only recently swapped to that from chick food as he's only four and a half months old. I also give them lots of scraps, frozen berries when it's hot (they've made it through some scorchers), corn when it's cold, and a handful of wheat every morning.
He looks to be well bred, from what we might call heritage stock. Most folks are used to looking at hatchery birds, which by way of comparison, are much, much smaller. We have the Frank Reese (Good Shepherd) line of Barred Rocks and they are incredibly large fowl.
As for the feed. It isn't ideal to feed a rooster a constant diet of layer with the high calcium. It can impact his fertility. When feeding a mixed flock, it is preferred to feed a product everyone can eat. Give the layers their calcium on the side, as in oyster shell, rather than being ground into the feed.