Board Thread:General Discussion/@comment-27213375-20160305063709/@comment-34258230-20180414005846

Asgore: Centuries (physically middle aged though), the reason why I say he is centuries old is because he fought in the war between humans and monsters.

Toriel: I would say Toriel is also a few centuries old, maybe the same age as Asgore, yet, just like him, she is not physically that old.

Asriel/Flowey: I would say around 13 or 14.

Chara: Probably around the same age as Asriel.

Frisk: Probably around the same age as Asriel and Chara.

Papyrus: Maybe between 19 and 25?

Sans: Maybe around 30?

Undyne: Maybe around the same age as Papyrus.

Alphys: Maybe around the same age as Papyrus and Undyne.