in my honest opinion, writing smut of characters who are underage ( or their ages are "ambiguous", but context clues clearly point to them being underage ) is just kind of a waste. there's almost always many attractive canonically adult characters. it avoids the controversy before it can even start.
with spiderverse specifically, literally just use their comics versions.
sure, the movie versions are soo cool and are more easily accessible because of the hype atsv is getting at the moment, but to avoid the age debate? write about the canonically adult versions of them that exist in the comics. a few quick google searches and skimming their wikis can give you just as much info as we have from the movies. and especially with pavitr or hobie or gayatri, who we barely get any actual information about from the movie? yeah, just use the comics. not only do we have more substance and backstory, but ( cannot stress this enough ) they're ADULTS! and since you as a writer do already fill in those gaps for gayatri since she barely has any character defining moments in the comics or movie, it shouldn't make a difference.
and granted, a lot of the appeal of the movies is that the designs are much cooler than in the comics ( looking at pavitr ). with that being said? they have beta suit designs, beta physical features from the movies that are just as cool as the final ones. push those onto the comic characters and boom, you have adult characters with cool designs who you can write smut about without issue.
Yes, I've thought about this as a comic reader, and I think is an excellent alternative (especially for Miles omg he's so cool in the comics and his personality is very similar but he actually acts like an adult, and I could go on, but I digress) and this works for Pavitr, but Gayatri doesn't exist in the comics, Pavitr's love interest is Meera Jain (she features in a fic of mine already but want to write more about her solo).
And on Hobie, I'd say his comic version is more clearly a teenager, where as ATSV Hobie appears to be on late teens/young adult (18-19) and comic Hobie is more aroace coded.
I think the only characters I'd write nsfw of (apart from the canonically adult ones) would be Pavitr and Gayatri but only because of the adult image of them I have in my head, and because of this, I'd feel uncomfortable knowing that are adult people using my writing to thirst over canon Pavitr and Gayatri.
I sincerely thank you for helping me with this. ( ◜‿◝ )♡ I think I'll refrain from writing that sort of content for them.