The word antique is not generally used in the philatelic world. You would never hear a philatelist refer to a stamp as antique. Classic would be the general term for an early issue, even though technically they may be classed as antique by definition of the word. Even this forum is divided into modern and classic. There's no "antique" forum.

It's just not used.
So while it doesn't really bother me, when I see a seller refer to a stamp as antique, I can't help but feel it's a bit dodgy. Either the seller knows nothing about stamps, or is fishing for non stamp collectors or perhaps investors who know little about stamps, trying to make it sound old and therefore rare and valuable. It's kind of like a used car salesman strategy

It would definitely put me off buying from them. A genuine stamp should sell itself if it's described accurately, without the need for fluff.
Balf