xp is correct. sir henry is 3.5 years old and has never brumated completely. every year he does turn into a lazy couch potato though, doesn't eat much, hides a lot, and in general does things that worry the hell out of me! but in the long run, he's just being a normal dragon and i have to tell my mind it can shut up!
They sure are different from one dragon to the next. There have been some dragons that are 5 or older
that have never brumated while some have gone into a brumation phase at 6 or 7 months of age.
I am really not sure what the causes would be as to why some do or don't but as long as they are healthy
that is all that matters!