Board Thread:General Discussion/@comment-27907368-20160604051050/@comment-27620479-20160612193624

Let's see:

At least some beings must age. Undyne used to be a child and boss monsters age when they have a kid of their own is already mentioned in-game. They may or may not die of old age, but there are certainly kids getting adults.

The monsters that became amalgamates may have fallen in battle. There were 6 humans before Frisk. Given that Undyne is overly hostile even if Frisk didn't kill (and she knows it), may imply that some of the other humans, probably reluctantly, fought back. Or it could have been an accident, or Flowey's doing.

Monsters have a tradition of burial, as described in an essay. If they didn't die naturally, it probably wouldn't be so important to be what seems to be a school assignment.

Even if monsters don't age, how does that extend to humans?

If we assume that Chara isn't a child any more, why Asriel is? Also, why would they choose to project a child's image if that's what they are doing? If they are an adult, and has the power to create their avatar, wouldn't it be more appropriate to choose something that is taken seriously, or fits their intention to erase the world?