Lots of prior discussion on this site -- you might want to do some searches.
Rounded off, and pro and con arguments reduced down, I have always understood it to be:
15 years in cold fresh water, 10 in cold salt water environments, and 5 in hot salt water regions.
Rationalization: No matter how old the standing rigging is on any boat, the owner can always justify ignoring it "for another couple years" on the grounds that it hasn't fallen down, yet.
No matter how young you think yours is, do be sure to inspect it every year for any cracked swages or broken strands. Brion Toss' excellent rigging book is a good guide on what to look for, BTW.
Holiday greetings,
Loren in PDX