Definitions for "antique" exist, but are different for different things. In general use, it requies that something be more than 100 years old. Obviously, until recently that excluded nearly all audio gear. For automobiles, it had another definition. For audio, there are no universally accepted definitions, but your list is pretty good, and one that many would agree with (except for the "retro" correction made by Wigwam. He's absolutely correct about that. It's an English word with a clear definition, referring to something actually new that is styled so as to look old or evoke nostalgia for an earlier period.) I doubt there is any list out there that everyone would agree with, so you can expect a few people to differ with any definitions.
Interestingly, at the Mega Show here this past weekend I saw a booth selling "retro" radios that were virtual clones of the old Bush radios, very popular in the 1960s in the UK. Just today I found an original Bush radio, for only twelve bucks. The ones in the exhibition were all retro; my newly-acquired one is old or vintage (but not yet antique). I would say both have classic styling, although only the original is truly a classic.