I was making the same assumption when looking for an explanation as to why my cockerels leave it late to start crowing. Digging a bit deeper, I've now come to the conclusion that our birds are normal and very young cockerels (chicks) aren't really crowing, whatever weird sounds come out of their beaks.
My reasoning is as follows. Chickens are birds, so what ornithology has to say about bird vocalisations is relevant. Ornithology usually distinguishes between calls, which are short, simple, usually single note/ sounds made by both sexes throughout the year (like alarm calls), and songs, which are long, complicated sounds produced normally by males only, with some seasonal and regional exceptions (Australasia, notably, and we've all read about crowing hens). So a crow is a sort of song. Song is said to have two principal functions, territorial defence, and mate attraction. Crowing starting up when the cockerel reaches sexual maturity obviously fits, being consistent with this. Our cockerels are behaving normally, no additional explanation required. Crowing in an immature cockerel is what requires explanation, assuming it is really crowing of course.