Joe, it depends on who you ask! For me? Anything before 1990.... doesn't make it a GOOD machine, as many of those have the nylon "innards", but I still consider them vintage.
Technically, the word "vintage" should be accompanied by a year...as in "Vintage 1950" or "Vintage 1986".... just as technically, it's not an antique until it's 100 years old...