alt Hacker News> planes that are simply too old
Planes don’t really age like that, at least not if they’re serviced. They’re constantly being rebuilt and inspected.
The only reason airliner fleets churn as much as they do is fuel efficiency and maintenance standardization.
Nit: at some point you start getting metal fatigue issues (see Aloha Airlines Flight 243) but in general yes: fuel efficiency and fleet standardization.
Also airliners usually just become cargo planes for quite a long time before retirement. Eg. there's a bunch of DC-3s still being commercially operated. Jet engine noise regs killed a bunch of early jets, but older prop aircraft are still going strong.