In case if you've ever wondered what technically defines something as vintage, retro, or antique (like I have more times than I can count...) you're in luck! I know I've been on the borderline for quite some time and it's nice to finally know the exact answer..
antiques: According to Merriam Webster, an antique is "a work of art, piece of furniture, or decorative object made at an earlier period and according to various customs laws at least 100 years ago." Make sure that if you're listing something as "antique clothing" that it is AT LEAST 100 years old (this is different with cars).
Here is an antique wedding dress from the 1900's my Grandmother Kutch gifted to me from her antique store called, "Plain Jane's Antiques"
vintage:Although widely misused, the term "vintage" refers to an item that is at least 20 years old or more (there you go, you 1980's fans!) I know I hate seeing it misused and overused because it is such a fanatic thing today for something to be "vintage." One of my teachers at school insists that the term vintage should not be applied to any object under 50 years old. This is currently up in the air, but at least twenty years is the accepted age to deem objects under the "vintage" category. True vintage could be categorized at least 50 years old. "New vintage" is a term I've heard describing 1980's barely vintage items.
Here I am wearing a vintage dress owned by my Great Grandmother Frisina in the 1930's and 1940's.
Retro: retro simply refers to anything that looks out of style for the current time period. This could be clothing that was popular in the late 1990's (not technically vintage, yet) or any new design that references designs or ideas of the past. This also seems to be somewhat interchangeable with the word, "vintage inspired." The 1970's are often referred to as "retro" although they are technically over 40 years old... which can be (in my eyes) considered "vintage."
Here's a dress I bought at Modcloth that is retro, or "vintage inspired."
I hope this cleared up some minor confusions for you like it did for me!