There's a convention for some things:

- antique = 100 or more years old;
- vintage = either between 25 and 100 years old or between 50 and 100 years old, depending on who you're talking to

Wikipedia asserts something rather different for old clothes, however:

- antique = pre-1920s
- vintage = 1920s to 1960s

As noted above, the accepted convention for dates relevant to 'vintage' cars is different again.

Take your pick… how long was that piece of string, again? Anyway, as far as eBay listings are concerned, 'vintage' seems to mean second-hand (any age): nothing to do with inherent quality, although sometimes a euphemism for old and tatty.