Talk:Monsters/@comment-31034341-20170113091033/@comment-27701762-20170113092121

There is no information in the game that explains how normal monsters age. They could age normally like humans, they could have different ages depending on what monster type they are (this at least is partially suggested by the existence of Gerson), or there could be some other form.

The only thing we know for certain is how Boss Monsters age, which is the specific species of monsters that encompass Asgore, Toriel, and Asriel. Boss Monster parents grow older with their (biological) children, so if the child dies (as Asriel did), then the parents stop aging.