This is how I see it. Of course it is only my opinion based on other people's posts on many different sites:
Retro 1980-1999
Vintage 1920-1979
Antique: pre-1920
It's a very subjective thing, and these are only guidelines I have found useful.
I'm sure there are those who have different definitions, and it would be interesting to get some more input on this topic. :-)