The definition is simple:
1: of old, recognized, and enduring interest, importance, or quality : classic
2: dating from the past : old
Used in connection with baseball cards, the word vintage conjures up images of great old cards.
What is the vintage cutoff for you? How old does a card have to be to be vintage in your book? Depending on your age, a 1988 Donruss card from the junk wax era could seem "old".
For me, vintage is any pre-1981 card. I started collecting in 1981. I bought Topps, Fleer and Donruss cards. Fleer and Donruss were breaking in on the Topps monopoly that year, so we had plenty to choose from and bought whichever brand we could find. We weren't choosy. So for those in my little circle, anything from 1980 and earlier was mysterious and much desired.
Even now, 29 years later, I still consider anything from 1980 and earlier to be vintage. They still hold the same attraction for me that they did all those years ago. I love the feel of the old cardboard in my hand. It just feels right.
Unfortunately, I don't own the Robinson or Yaz cards pictured above. I do own the Smith card. One of these days, I'll be able to say that about the Yaz too.