Watching the episode again, Spike's throwaway line in this scene is: "Are you that one creaky grandpa from Ponyville Retirement Village?"
So here's a crack fanfic idea for ya: That one creaky grandpa IS an immortal Star Swirl the Bearded leading a quiet life. FANFIC COMBO: It isn't actually Star Swirl, but a kooky old man who emphatically believes he is. TRIPLE WORD SCORE: It actually is him, but he's so old he forgets now and then.
Cut, print, off to FiMFiction's featured list. (Not Equestria Daily, though. It wouldn't stand a chance.)