The knob and tube wiring in my 1930's house was still working fine. That tech would need to be updated for modern safety requirements (ground wire, etc) but worked without plastics for about 50 years. Much high cost though, I would guess.

Old wire is usually fine if it just sits there, but it may no longer be water proof or turn hard and brittle. That's why the failure mode is so unfortunate, it loses the properties you'd want in an insulator while still appearing safe.

Of course you're ignoring all the houses that burned to the ground because knob and tube sucks.