For instance, look at this auction on the 'bay. Maybe I'm crazy, but when I use the term in a music gear context, I use it kind of like one refers to better wines. An '01 Laffitte is vintage, while an '01 Gallo is turpentine. I mean, there's nothing wrong with an LXP1, really, but it is to effects as Gallo is to wine; it'll get you drunk, but you'd really rather be drinking something better.
In that light, I submit that there is no hard, fast "vintage event horizon," a specific date, and if a piece of gear is manufactured before that date, it is vintage. Vintage is rather a descriptor, and means the same as "desirable," I think. Or "has a certain something" or "peer reviewed and approved." And that's the difference between something vintage and something that's just plain old.