To me, vintage cymbals mean mid-1960's and earlier. Most of the cymbals that ZIldjian offers to this day originated in the late 1960's/early 1970's....and pretty much still sound the same and I consider this to be the start of the modern sounding cymbal, same with Paiste.
I love how people try to search out "vintage" Paiste 2002 black label cymbals for that "Bonham sound" (and spend ridiculous amounts of $$ doing it too!), when you can buy the same cymbal today with the red label and it will sound exactly the same as those early ones.
Like others said above, even though early 90's would now QUALIFY as vintage as far as actual age, those are modern sounding and looking cymbals, period. Most of them can still be had new to this day.
My ultimate definition of a vintage cymbal? The A Zildjians from the mid-1950's that Joe Morello used with the Dave Brubeck Quartet when they recorded Time Out. I have yet to hear anything modern that sounds remotely like them, and those were some nice, sweet sounding cymbals, hand picked by Mr Avedis Zildjian himself for Joe Morello. Yes Sir