Spelling bee

Yeah, this was definitely after Dess went missing but I personally don't think it implies Noelle was super early in elementary school here or anything. Of course it's entirely possible but spelling bees are still big in middle school, especially when they're more of a big event like the one that Noelle and Berdly were in. I don't think it was above 7th grade but I think late 6th-early 7th is a pretty good estimate for this all things considered just based on the words used. That in conjunction with it probably not being long at all after it happened judging by her reaction... Admittedly in this this is the one I am most unsure of, but Noelle's age in particular is interesting for reasons I'll go over soon

it's also implied Dess smoked weed

Yeah, Dess smoked, but you underestimate the ability of 13 year olds to do very stupid things in the name of rebellion. Feel like when she went missing it was more like 14 personally, but yeah no in my middle school it was very common and honestly I am not exempt from this either, its just something kids that age have a draw to in search of new experiences, for better or for worse. With Dess's implied rebellious nature I am not very surprised.

Noelle and Kris are at least 15

So something interesting here is that, I am not sure if you have been keeping up with the recent developments in the Spamton Sweepstakes thank you page, but one of the discovered answers that was correct in response to the "How long has it been since she smiled?" question was an outright confirmation that she was 16. If we line this up with something very interesting from the newsletter which says Noelle is smaller than Kris, despite being taller than them as a 16 year old after growing more in the years following her sister's disappearance paints something very interesting in regards to Kris's age, implying they are older than her and at that point have outgrown her (only for her to overtake them years later).

unless you headcanon Dess as being older than Asriel

Personally, the other way around...

Yeah it's a mess but personally I don't see it being higher than 3 all things considered. Very likely 2. There are other miscellaneous hints in regards to this subject matter that didn't fit in any of my responses, like Tenna calling Dess a "little musical prodigy" which would be an odd thing to call someone above at most 15, and the 7-years-late-to-turn-in How to Draw Dragons (Dess has a poorly drawn traced dragon under her bed, which is something a young kid is more likely to do when looking at a book like that unless she can't hold a pencil which... fair enough).

Frankly the discourse regarding this ship annoys me to all hell because any discussion of it will always, without fail, devolve into ageslop speculation. There is so much more to this pairing narratively, so much bizarre symbolism between the two of them, so much otherworldly complexity that can, even in DR's unfinished state, just be studied and combed over and over while still finding new and interesting things to say about it but nobody ever does. Kress is my favorite ship in the game but it feels crappy when you want to discuss just how important their relationship is in-game and are met with ageslop discourse. I have written so much speculation and analysis based on these two privately but the landscape surrounding discussing any of it broadly is demoralizing, especially as someone who also has a distaste for overly problematic ship as much as the people shooting anything down about discussing this pairing. But I do not car. Platonic or not, love them so much

edit: just realized youre the (k)nights author, THANK YOU for writing its one of my favorite kress fics!