They won't all go broody, esp hatchery stock (where they're bred for production more than natural setting). They're simply more predisposed to it than other dual purpose breeds. The oldest I've heard of a hen deciding to go broody was in her 2nd year.
I have a line of barred rocks that go broody, craziest thing! (they aren't supposed to be setters) Even the offspring from this one hen of mine, located in CA, are going broody haha.