There are many different terms used to describe books, but they are also frequently mis-used. The differences between antiquarian, vintage and collectible are the most important to understand.
The term antiquarian can be used as both a noun and an adjective. It can refer to a variety of antiquities including rare books, hence physical objects, and is also used to refer to students, dealers and collectors of antiquities. Generally speaking an antique is considered to be an object over one hundred years old and therefore many books of similar age are widely classed as antiquarian. However, this is not strictly speaking so: Purists consider an antiquarian book to be from the seventeenth century or earlier - rare old tomes for which demand outstrips supply. In contrast, many books from the nineteenth century were mass produced due to advances in production methods, and sufficient quantities have survived to ensure that supply outweighs demand.
This is important for collectors to understand: The age of a book does not necessarily make it antiquarian in the purist sense, nor does it guarantee a book will be of any great value.
The term vintage is also frequently used to describe the age of a book. In its purist sense vintage is considered to be between fifty and a hundred years old, but like so many such terms the meaning has been stretched in recent years by inexperienced sellers who might consider a twenty year old book to be vintage. As with antiquarian books, vintage does not necessarily denote any great value. The word is merely an adjective and ultimately the laws of supply and demand, the condition and any special features of a book, will determine its value.
Collectible is another term which is frequently abused. The generally accepted rule is that for an item to be collectible it should be worth more than its original price. A book you buy for twenty pounds today which nobody else wants to pay more than two pounds for tomorrow, is not collectible, but may be offered on the second hand market as being so. A nineteenth century mass produced work of fiction, is most likely not collectible, nor a four hundred year old religious tome which long since failed to capture the interest of readers. In contrast, a cheap first edition paperback which quickly went out of print, will likely be worth many times its original price - subject as always to those laws of supply and demand, the condition and any special features of a book.
Modern marketing has seen a trend which further redefines the word collectible to include new items. Book collectors need to remember: That which is still in print, still in the shops, still in publishers and wholesalers warehouses, will not be collectible - no matter what the marketing blurb might say.