I bought a couple of boxes of Sancho Panza MM Quixotes when I was fairly new to the hobby. I let one rest for a year and tried aging the other for 3 years. Discovered that Quixotes have an expiry. The rested box was great; the aged box lost a lot of flavor.

Currently I'm aging one Cohiba lancero for retirement. That's one STICK, not one box ... I think I put it away in 2012. I know it's marked with the acquisition date, but I don't remember it offhand and I'm not going to go dig it up to check. So, another 6 years to go.