I think we really need to treat people like adults. If someone deletes a post after others have responded, their post is usually quoted in the response and thus is preserved anyway. Maybe a 24 hour limit if there must be one.
I sometimes realize after edit time is up that there are errors - especially if I write on my phone. It is frustrating to have errors that make me look illiterate preserved forever.
I am on other fora and they have permanent editing. It is exceedingly rare for people to delete or otherwise molest old posts for nefarious reasons. It is my single biggest dislike about posting here.
Sometimes people put links to stuff that then vanishes - it would be nice to be able to delete those links or replace them as i have on other fora.
I frequently have people respond to posts i made 3 years ago. No reason I should not be able to fix a broken link (for example) from back then.
Maybe when the site started it was more kids, but now most Buffy fans are adults.