Anecdote time:
Some of you will remember when McDonald's was a drive-IN. You could get: Hamburgers, cheeseburgers, french fries and milkshakes. They used to actually fry real, quality hamburger meat and toast the bun so it was nice and crisp and...tasted good.
McDonald's is still around, but it's not quite like it used to be back then. There are more items on the menu, but the overall quality has dropped. The main thing about McDonald's, now, is that it's cheap, quick and convenient. The "novelty" of the drive-in is gone and replaced with the drive-THRU (through).....and quality be damned!
So, how does this relate to the question of "What makes it vintage"? Well, I'm hoping that it shows that "vintage" relates to the magical (and now almost mythical) time when there was more of a drive to be unique within your given industry -be it hamburgers, cars, furniture, houses.....or drums.
Things like individuality and uniqueness became too costly. And, when Asian brands showed that they could produce high-quality drums for less money, it became the swan song of American brands forever after.
It was a matter of "If ya can't beat 'em, join 'em!" after that. And that's why even American made drums, now, look like anything else out there. Most of the components of all the drum brands are made at the same factories in China. The only thing that signifies any real individuality, now, is in terms of branding. Nobody is "making" drums in Elkhart or Chicago or Fullerton or Dayton. It's all coming from Taiwan.
I would say that if you can understand the era, then it's very clear what separates non-vintage drums from vintage. But, when it comes to formulating a clear definition of terms for everyone else, it can be more ambiguous. In terms of drums, it doesn't just have to do with the chronological age; It has more to do with the period of time when America's perspective on "How things are done" changed.
Now, just like with the expanded menu at McDonald's, we have more to choose from than ever before....but none of it seems to have the same appeal or "fun" to it. It's just another commodity that has been taken for granted. We're bored with all the shiny new toys we can easily get our hands on. We still have the most fun when we're poppin' wheelies on our old stingrays! Now, THAT'S vintage! ;)
/rant