I'm far from an expert, but I both collect and sell costume jewelry.
Hopefully I can speak with a little bit of authority.
The term "vintage" really doesn't mean much in the big picture. (A
coprolite is vintage poop, for example. ;-D ) But it can help when
selling on Ebay. "Antique" generally means if an item is 100 years
old or older, but most people I know of don't refer to jewelry as
antique. Vintage when used in reference to jewelry generally means
"of and about that time period" which helps differentiate a piece
from a recent reproduction.
Of more importance is to determine the time period in which the
piece was produced, the maker (if known) and the style. Those three
things, along with knowing the materials (silver, gold kt., type of
stone, etc.) will help you get your best price.
"Answers to Questions About Old Jewelry 1840-1950" by C. Jeanenne
Bell, G.G. 5th ed is a wonderful resource if you need help
determining which period your pieces fit into.
If you need help identifying pieces, feel free to send me pictures
and I'll give it my best guess. (If you have a flat bed scanner,
sometimes you can get better up-close images.)
Do you know how you are going to sell your jewelry? I can also give
you some pointers if you want to sell on Ebay.
All my best,