Do cables age or become too old at any point?

All copper oxidizes with age. This is pretty easy to tell though, as if it is still relatively shiny, it's still "fresh". When it is getting darker and loses brilliance, it is time to either replace or reterminate. Sean
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The copper inside a cable's jacket is not expose to air and therefore cannot oxidize. It should be fine for a very long time. When you buy cable it does not need a "freshness date".

Only if you are using bare wire, the exposed ends as Garfish mentions can oxidize. The ends can be tinned with silver solder to stop the oxidation. Silver will oxidize, but is still a good conductor. Those ends can always be re-done every few years. You'll only lose an inch of cable each time.

If the cabes have copper spades connections, etc, they can be cleaned (as per Garfish).

Sugar, have you ever looked at the color of the copper in some clear jacketed "monster" type cables after a few years and compared this to brand new cable ? It is definitely darker. Some of this has to do with the type of materials used within the jacket itself though. The plasticizers in the jacket tend to "leak out" and taint the conductors. One would have to use what is called a Type II mil-spec jacket to alleviate this type of problem. Even then, corrosion would set in over time as nothing that is man-made will last forever. For all practical purposes, this would take a LONG time though, especially if the open ends of the cable were properly prepped i.e. "sealed".

I do agree that wire that is exposed will tarnish FAR, FAR faster than wire that is protected, especially when exposed to varying levels of humidity. Sean
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I hope there is some assumption of quality. Just because 25 cent per foot Monster cable oxidizes in the jacket, does not mean much. I would not consider that monster stuff air tight. It is pretty easy for even a child to pull the copper wire out of the plastic cover of Monster cable with a pair of pliers. Try doing that with a run of JPS Labs Super 2s, or any high end cable. You could tow a train with some cables.

The capacitors in a $79.00 KLH receiver from Circuit City may go bad after two years. It does not imply that the caps in a $20,000 pair of Mark Levinson mono-block amplifiers will go bad that soon (or any other high-end gear); and we better only buy new stuff.

Yes cables become too old at some point. I had two pair of very old Purist cables, one was 10 feet long, the other 8 feet long.

I placed them in a dark cozy environment for several days, hoping for a baby Purist cable (at least 2 feet long), but even with Handels' Water Music playing softly in the background (their favorite) NO BABY CABLE.