Years = meaningless
My wife gets two years out of a chain, because she rides about 2,000 miles a year, doesn't ride in the rain, isn't heavy, and doesn't put out a ton of power. A meaningful number is to say she gets 4,000 miles out of a 10-speed chain.
I own a single component with over 18,000 miles on it: a Thomson Elite seatpost. I would never expect any wear item to last that long in my use, least of all a chain.
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