"[W]ith the recent passing of Ernest Borgnine (Marty, 1961) and now Celeste Holm (Gentleman's Agreement, 1947) today..."

"... who is now the longest-ago Oscar winner in each of the five major categories who's still living?"

For Best Actress, it has to be Luise Rainer (The Good Earth, 1937). She's still chugging along at 100+.

ADDED: I mostly know Celeste Holm from "All About Eve":

"I walked onto the set of 'All About Eve' on the first day and said, 'Good Morning,' and do you know her reply? [Bette Davis] said, 'Oh shit, good manners'. I never spoke to her again - ever."