Well built vintage electronic circuitry can last a very long time, as evidenced by the number of Hammond organs that are still working, some from as far back as the 1930s. Hammond's engineers designed their vacuum tube (valve) amplifiers conservatively, putting minimal stress on the components. All but one of the tubes in my 1962 Hammond M-111 is original and I have no intention of replacing them unless one fails.
However, one type of component that is prone to wearing out, regardless of how little or how much a piece of equipment was used, is the electrolytic capacitor.