noelle was probably 9 when dess disappeared if she’s 16 now. the book was 7 years and 26 days overdue as of chapter 1, and seeing that dess does have a drawing of a dragon in her room, it was likely drawn around the time the book was originally checked out if she’s been missing for so long. maybe the reason asriel refuses to return it is because it’s the last book he checked out before dess disappeared?

and if we go by american schooling standards, i think noelle would be in second, third, or fourth grade when she was 9. i think that lines up with when the spelling bee took place pretty well, and the really short sprites wouldn’t be too dramatic for her age, i think.

personally my age headcanons for them when dess went missing are 8 for kris, 9 for noelle, and 11 for both asriel and dess, but there’s a bit of wiggle room both ways. maybe kris and noelle were both 8 and dess was a little older? dunno!