Most equipment used by man in the course of his commercial/personal use or activities become obsolete when newer or more advance technology has taken over. But in the world of Aviation there is no such thing as an obsolete aircraft. Any aircraft regardless of its year model is deemed AIRWORTHY as long as it has complied with all the rigid inspections on the engine and airframe (Airframe & Powerplant) as dictated by the aircraft manufacturer's manuals and mandated & approved for flight by the Federal Aviation Authority (FAA), if it was an American made aircraft. If you attend airshows in the USA you would see many vintage aircraft of the WORLD WAR I and WORLD WAR II era still flying great and are all in pristine condition.
As long as the airplane is maintained and kept within the given parameters of manufacturer's specifications then there is NO such thing as OBSOLETE AIRCRAFT.