What does vintage mean when used to describe a bike?

Originally vintage referred to the year a wine was produced, as in, “a red table wine of 2003 vintage”. Today it is commonly used to describe when just about anything was produced, such as, “a Schwinn vintage 2014 bike” or “a vintage 2014 Schwinn bike”. These I understand.

But what does vintage mean when used to describe a bike with no year of production provided?