So a civil war repro sword made in 1985 would be vintage?
The value doesn't have anything to do with it's being vintage in most cases. It's a descriptor to give you an approximate age to the piece. Sometimes vintage is worth less (a vintage Saturn station wagon) vintage clothing would refer to the age, and says nothing about the perceived value.
Value is based on 3 things: rarity, popularity, and what you can get for it in your market.
A $500 delft plate isn't worth $500.00 until you can sell it.
Browse through ebay, Vintage doesn't mean a thing. That could be from a year ago and people are calling it vintage.
I always went by 20 years vintage and 100 Antique.