Take it and have it inspected by asking if you can trade at a welding supply store. Usually, they will take them since they have no money in them when they trade them to the gas company that actually fills the bottles. I walked in with an old one and they swapped me right out only having to pay $19 for 25# of CO2. It is only $35 for a 150# fill, but I can carry a 25#er. They had no problem that the bottle came from a different state or how old it was. As long as it isn't ancient I think you will get swapped for a newly tested tank. I wouldn't use that old of a tank if you aren't sure about its safety (and I am not a anally oversafe type of guy either), it just isn't worth the destruction that can happen with that big a "bomb". A few people on here say they have no welding supply stores around them so you may have to check fire extinquisher places, but either get the bottle tested or swap it so you don't have that worry.
If it's a steel tank, they last until they fail hydrotest - my 5# tank has hydrotest stamps going back as far as '67, with the most recent being 01/07. The valve was replaced at the last hydrotest, before I bought it. In other words, they last a LONG time if you don't abuse them.