Antique? Vintage? What You Need to Know ....
An important part of getting started is to learn the "language" of antiquing. Although some will use the terms loosely, there are generally accepted guidelines around how you characterize or describe an item you are offering for sale. One set of terms to remember are Vintage, Antique, and Period.
Vintage items are typically 50 years old or more, but less than 100, and may not be attributable to a specific period. Antique items are over 100 years old, and an item described as a Period piece is dated to a specific reign e.g. Louis Phillipe or stylistic period e.g. Arts and Crafts.
Vintage is often used quite loosely to describe things which are old but not antique. "Old" can be as little a 20 years in some eyes. Similarly, Art Deco items which are strictly (from 1920's to '30's) not antique, are still classified as such. So the lines can be blurry, but should never intentionally set out to mislead.
Pay attention to how a period piece is described. For example a "Louis XIII style desk" is not likely to be from that period (1610-1643), but from a later date in the same decorative style as that period. If it was labelled "Period Louis XIII desk" you should be able to verify that the construction, patina and wear patterns (and price tag!) are those of a 200-year old piece.
Lastly, remember that old does not equal good. Fine antiques were expensive when they were made. Inferior pieces over time just become older trash. Rely on your own judgment to verify that the materials and craftsmanship look like those that would be appropriate to someone's treasured possession and worthy of the title "antique".