Planes don't age in the same way cars do. There is a maintenance schedule that inspects and replaces almost literally every component at some point. So the engines on these planes can be just a year old for example.

And the military has a tendency to also upgrade the avionics and capabilities at several points in the lifetime of a program. So there is a lot of tech in these planes that's much newer than 60 years old.

Aged out weapons design is a flying target.

War profiteers say motherhood statements about the crew but don't care.

60 years of new weapons design opportunities was pocketed in pork by the politicians bought and paid for.