How old do you think the main characters are, based on their behavior and the information provided by the show? Biological age, though. Eclipsa's age would be 200+ if otherwise.
Marco: 15 as of Lava Lake Beach
Tom: weirdly enough there’s no reference to his age, even among tweets by the crew as far as I could find, but according to Star in the Book Of Spells he’s “close to her age”, so no 100 years old teenage looking demons here. This is not Twilight. Or an anime. Likely 15 or 16.
Pony Head: according to an old tweet by Daron she’s one year older than Star, so she’d be 16 or close to 16
Moon: I’d say in her early mid 40s
River: looks older than Moon at times, especially in the close ups in Camping Trip (likely for comedic effect), but we know they have the same age, so he’s probably in his early mid 40s as well. Or 17 felled stags according to the Johansens’ calendar
Eclipsa: probably younger than Moon since she became Queen at an early age and Meteora was just a baby when she was crystallized. I’d say early 30s.
Ludo: even if in some episodes he looks like a old man he’s probably around 30, since his parents are still alive, he has several older brothers, and Dennis looks like a late teen but old enough to remember him before he left home.
Glossaryck: as old as as the Universe but also not quite as old
Janna, Jackie, Alfonzo, Ferguson and all the other teens from Earth: they were in class with Marco and Star so they’re all 14-15 depending on how early or late in the year their birthday is.Â
Buff Frog: given how fast his kids are developing I wouldn’t be surprised if he turned out to be 8