In its more than 125 years of history, the Victorinox Swiss Army Knife has become a model of durability and dependability. As a result of its rugged and rich heritage, the knives have become as highly desired by collectors as they are to those who actually use the tool. There are many ways to estimate the age of a knife.
Verify that the knife is a genuine Swiss Army knife. Swiss Army knives are usually easy to spot: Look for the Victorinox "cross" logo or (on military-issue knives) the coat of arms of Switzerland. However, these identifiers could have come off or been removed from a genuine knife or the knife could have one of the symbols but still be a fraud, so it is best to get the verification of a knowledgeable, trustworthy knife collector or antique appraiser.
Look at the physical characteristics of your knife: color, shape and blade style/count. The knives have had only a handful of makeovers throughout the company's history, possibly because aesthetics weren't a top priority. Still, during its over-100-year run, the knife has made a few noteworthy changes.
Review the following to get a starting point to making an estimation on your knife's age: The original 1891 model was brown and about 4 inches long. A reproduction was made recently. The Swiss Army knife was not "spring-loaded" until 1897--that was the first red-handled model. The spring is what enables it to have multiple tools on each side.
Because the knife's designs have varied so little, to learn of the knife's precise age it will take more than just comparing descriptions of the knives to your own.
Contact an appraiser if you the knife piques your curiosity, and you are willing to invest more time and energy into the tool. You could find a local antique shop that specializes in tools or photograph it and email an appraiser on the net. Many appraisers will do this for free, but there also are professionals that charge a fee of about $5 or $10.
When searching for a local appraiser for your knife, look for an actual business that has established a history of giving this service.
As with all antiques, don't sell anything to the very first appraiser you see about the item. They could be attempting to give you an unfair deal, especially if they seem forceful or try to rush you into selling by threatening their offer won't stand long. Get a second, possibly even a third, opinion before selling.