Old airplanes wear out or corrode out. I was badly injured when a 40 year old King Air suffered a fuel pump failure. A skipped inspection almost killed us all!
After 3 -ish years, the factory's liability fades and then the reliability of any machine becomes increasingly dependent upon the thoroughness of the last mechanic.
For example, if the owner does 1,000 jumps per year - in the Southern California desert - a parachute might be scrap after 3 years.
OTOH Closet Queens might be in mint condition after 30 or 40 years. However, Closet Queens may need Special Inspections or Service Bulletins that were published long before the interweb became popular. That is why young riggers should not feel forced to repack any parachute older than themselves.
As for the grey-bearded, grumpy old Master Riggers ... I refuse to repack plenty of gear that was fashionable when I started jumping: round reserves suspected of acid-mesh, first generation 5-cell square reserves, Sentinel AADs, pre-3-Ring canopy releases, etc.