Ow, it hurts my eyes.
I would guess, perhaps, both options apply. I've always seen him as a much younger Sharptooth than Chomper's parents, as well as a different species. He doesn't (I'm assuming) have kids, nor a mate, so that might explain why there could be an age difference. Or maybe he's a lone wolf. Whatever floats your boat I guess (some pun intended. geddit haha). Also, it seems kind of obvious, to me at least, that he's a different species than Chomper's parents. So that could also be a possibility.
Real talk tho, he was an actual spartan and one of the most threatening Sharpteeth (Sharptooth, Sharptooths (plural?)) in the sequels. Maybe they just wanted to distinguish him.