Rule of thumb is about 7 years.
Much depends on where the boat is and what kind of stainless steel your rigging is made of. I just replaced the standing rigging on my Catalina 27. Boat US had an excellent article on rigging failure earlier this year. They have a very informative web site.In far northern latitudes, where the temp is cooler, less corrosion takes place than in warmer places (i.e. Seattle versus Miami). All marine stainless steel is not equally corrosion resistant. Type 304, commonly used for rigging, is less corrosion resistant than 316. Type 304 is somewhat stronger, however.I would suggest that you get a good, strong magnifying glass or loupe and look closely and intensely at your rigging, just where the wire enters the swaged fitting. This is where corrosion is most dangerous and failure is most likely. If you can see any cracks in the swage at the wire, or pitting in the wire, or if any wire strands are broken, replace it ASAP. The bottom fittings will usually corrode before the upper fittings, because they collect salt water and retain the water and salt in the fitting. You can buy dye kits to rub on the wire and swage that will show cracks and pitting more easily, but in my experience a good magnifyer will show the problems unless one has vision difficulties. If you see no faults in your fittings or wire, it's a judgement call whether to replace. Seven years is the rule of thumb for replacement. When I got my boat two years ago, the former owner couldn't tell me when the rigging had last been replaced. Upon close inspection with magnification, as above, I found cracks in the swages and pitting in the wire. I replaced the rigging myself, buying the wire and Norseman terminals fron a reputable rigging vendor. It is not exactly easy to do the work yourself, but if you are handy with tools and mechanically inclined and determined, the job is well within your abilitiess and will result in enormous satisfaction and confidence in your boat.You can put a drop of WD40 into each swage at the wire-swage connection to slow corrosion if your rigging is sound.