Board Thread:General Discussion/@comment-27324545-20160105135410/@comment-35443428-20180429181713

Here's what I think and my logic behind it

Frisk: 14-16 because if they were any younger I don't think they would be able to carefully craft a plan to either WIPE OUT AN ENTIRE RACE or save all the monsters

Sans: 18-22 because it's implyed that he did work at a lab once, but not for too long, another reason is that he's SUPER lazy(heh, like me) and I don't  think a middle aged skeleton would be like that but if he was a teen he wouldn't be a sentry

Papyrus: 16-18 just a bit younger than Sans.... I have no logic, just a guess

Toriel: 45 physically. 1000 in reality, we know that she was around to see the war so that happened I'd say AT LEAST 850 years before undertale

Asgore: 60 physically. 1050 in reality

Chara(before death): 12

Chara:(presently): ageless but looks 13

Asriel: same as Chara

Flowey: Immortal

Undyne: I'd say probably 21-25

Alphys: 22-24?

W.D. Gaster: 666 or 6666

Mettaton: Robots have no age but I'd say he's programmed to act 21

Muffet: 25-30?