I wouldn't be surprised if "Chanson de vieux amants" is in fact the same song Denver recorded in translation as "The Old Folks." but that's only a suspicion. I'd forgotten about "Angel" - it is indeed about growing old ("I am an old woman ....")

Not the real Buck (but I qualify for the "Plump" part; "stately"'s a judgment call though.)just a Joyce fan. Was once in a band, and we spent an entire evening (and several jugs of E&J's best) thinking up names. "Buck Mulligan Band" got the nod, and as I was in front, I was often mistaken for "Buck."

What about Kristofferson's great "Casey's Last Ride?" It's not strictly about getting old, I guess, but about maturing out of a relationship.

Or "Are You Tired Of Me, My Darling" which I think dates to the 1830s (Nanci Griffith did a smashing job on "Other Voices ..." with Chet atkins on acoustic 6 string. "Tecumseh Valley" by Townes van Zandt on the same disc is kinda about getting old (and then stopping getting older)

Stan Rogers did a nifty job with "Lies" though again, that's not about getting "Really" old, just getting on in years and on with life. On his "From Fresh Water" there's "The Last Watch" which deals with obsolescence, human and mechanical. I think that'd qualify.