More than 5 years seems good as a general rule, but I admit to exceeding that # fairly often. See last Summer's Clunker Challenge 100, beginning at post
#28 for probably the oldest I've ridden:
https://www.bikeforums.net/classic-v...100-4-a-2.html
They rode fine for 100km, but I kept my speed down on descents. I then mounted the new Kenda's on alloy rims and rode another 100km. The 45 y.o. Michelins had a better ride(on steel rims) than the new Kenda tires on alloy rims. Those ancient Michelins are leaning against my shop wall now, still holding air. Non-fixie tried some old sew-ups but had a side-wall failure. Don