What is vintage clothing?
Vintage clothing is defined as previously-owned clothing, that with age, looks better and maintains style.
Time is not the only criteria used to define vintage, but rather other elements such as enduring style, perceived quality and accrued value.
Vintage clothing usually comes from a different era, but the definition should not be confined only in years.
Why call some used clothes “vintage”?
In fashion, we take the term vintage from the culture of wine. Much like you can have a great vintage wine from a few years back, so too can you have a fantastic piece of vintage clothing that is not technically that old. Like wine, vintage clothing gets better, intensifies in quality and gains 
value with age.
Some pieces of clothing, that are rare simply because of their age, often transcend the definition of vintage and move into the category of antique or even historical artifact.
The value of these items illustrates that with time, vintage clothing can become rare and therefore more sought-after and expensive as a result.
thanks, this explanation was pretty helpful for my dissertation.