Board Thread:General Discussion/@comment-27324545-20160105135410/@comment-33238985-20190920202958

I'll add to this with theoretic ages, none of which will have one exact number.

Frisk: Most likely around 10, they're probably a tweenager.

Flowey: If we're talking how long Asriel has been a flower, I'd say he's chronologically centuries old with no physical age.

Napstablook: Too hard to tell, since he's a ghost. He could be as old as the Dreemurrs, or as old as the skelebros. Who knows.

Toriel: Most likely 1,000+, since she was very likely alive during the Humans vs Monsters war. As for her physical age, she's probably in her 40s or 50s.

Sans: Since he and his brother are skeletons, their chronological ages are very hard to pin-point. Sans is most likely in his late 20s or early 30s physically.

Papyrus: Probably in his early 20s physically, and as said before, his chronological age is difficult to figure out.

Mad Dummy: Same case as Napstablook.

Undyne: She is definetly older than Papyrus, and could be around the same age as Sans physically. She could be a good bit older chronologically however, as monsters seem to have a different physical aging pattern to humans. If only the Dreemurr family applys to this rule, then she is probably the same age physically and chronologically.

Alphys: She is most likely a little younger or older than Undyne. For an exact number, she could probably be in her late 20s/early 30s, similar to Sans.

Mettaton: Robots have no age at all, while the age of a ghost would be nearly impossible to figure out. So, his age remains a mystery.

Muffet: Hard to figure out. If we go by an accurate guess, I'd say she's in her early-mid 20s.

Asgore: 1,000+ chronologically, as he must have been alive during the war. Most likely in his 50s physically.

Asriel: About the same age as Frisk when he died, though he had lost his aging when he was reincarnated as Flowey.

Chara: Same case as Asriel, although they could've been a little older or younger than him when they died. Is chronologically centuries old like Flowey, although they were only reawakened once Frisk fell into the underground. If this is considered to affect their age, then they could be much younger than Flowey chronologically.

W. D. Gaster: Tricky, as he was erased from existence, which would make him timeless. If I were to guess, I'd say he is the same age physically and chronologically as Asgore.

The Annoying Dog: Who the frick knows anymore.

Temmie: Same as the Annoying Dog.

There are my thoughts on all of their ages, I hope you liked this. :)