I think it is quite common to find a 20 or 30 year old boat with original rigging. It is something that is often ignored by the original owner and subsequent owners. My 1977 CS27 has original rigging and will get a new rig including turnbuckles this year. If a boat is not raced or run hard there is a good chance that the rigging will look ok to a casual eye even after many years. But as Tommays says replacement is good for piece of mind. 12 to 15 years seems about right for a boat that is used seasonally.
Living aboard in Victoria Harbour