Vintage clothing is clothing that is at least 20 years old. For example right now clothing from the 80’s would be considered vintage. Anything older than that is also vintage.
Beware of “retro” clothing (on places such as eBay) as “retro” means “in the style of vintage” but is actually new. Some of these items are done quite authentically, but lack the same fabrications and details that a true vintage garment will have.