Continuing the discussion of monster ages: it's entirely possible that certain races of monster have variable life expectancies, like how different animals have different ones. Gerson is obviously based on a tortoise, an animal that, at the most extreme, can live to be over 250 years old, so who's to say that tortoise monsters don't have a similarly extended lifespan?

Yeah, that’s my thoughts on it. Since he’s a tortoise monster, it’d make sense he had a super long lifespan. And the other monsters may have a variety of lifespan lengths depending on what kind of monsters they are, where and how they live, etc.