line storage?

I can't say exactly how long line will last. You are storing it properly. I use line regularly that is 3-4 years old. A lot of line sitting on the shelves at some tackle stores is old. I always test the line I'm spooling by wrapping around my hands and pulling. This is a crude test, but line that has been compromised will fail with little pressure. I have seen 20# test break like its 6# test.