Yes, it’s a geeky thing, but Delta retired the last of its ancient DC-9-30s last week, sending N8928E from Providence to Delta, then into retirement. That particular aircraft was built in 1967 (oh, the glory days!) and spent the first 24 years of its life with Eastern Airlines, then joined Northwest in 1994 (perhaps it took a hiatus for 3 years in there, it’s not clear).
Dorks like me love the DC-9 because a) it’s a piece of aviation history still flying around; b) you only have a 20% chance of being stuck in a middle seat; and c) with the engines way in the back, the front of the plane (even in coach) is delightfully quiet.
Delta is still flying plenty of -40s and -50s, and several other airlines fly later variations on the DC-9 (MD-80, MD-90, 717), but the old -30s show that a well-maintained airplane can pretty much fly forever. Or at least 43 years.