It depends: First, how old is "older?" And would you be satisfied with a general overview, or do you want too know the exact year something was made?
There are reference books that cover a particular manufacturer in detail (Winchester, Remington, Colt, Smith & Wesson, Ruger and so on. And there are books that cover certain popular models (Colt Single Actions & 1911 pistols, Winchester lever action rifles, etc. But no one book covers everything in finite detail. If there was such a thing you couldn't lift it!
For a more general overview two books are handy - and the give you a general idea about prices, although what they show is an average. Particular guns may sell for more or less in your area.
These books are:
"The Blue Book of Gun Values" by S.P. Fjestad. (Blue Book Publications, Inc.)
"Flayderman's Guide to Antique American Firearms" by Norm Flayderman. (Krasue Publications.)
They won't do everything but they will give you a start.