Do cables age or become too old at any point?

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).

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.

Albert: Next time try wine, candles, and Ravel's Bolero.

I completely agree with you Sean and others. It is just my opinion that the typical generic "clear" jacket cable is so poorly made, it is going bad the minute is leaves the factory. I would not recommend it brand new, so used is a non starter. On the other end of the spectrum, I have re-terminated older high quality cable. When I cut the ends off and stripped down some of the covering, the copper cable under there was as shinny as new.

Quality cables is a recent event. Most cable brands out there are less than five to seven years old. I would not consider any of them old yet. Some of the very oldest MIT music hose from 1985 may be a risk, but has anyone cut then open or tested them to see? The MIT Terminator series only started in 1994 (white jacket); the ones with the grey jacket are only a couple years old at the most.

The original poster did not specify copper cable. Silver cable is another story completely. As well as silver/copper strands like Nordost and others; and gold/silver cable like Siltech. These types of cable should last a lot longer than copper. It is my understanding that silver is still a good conductor when it tarnishes. Gold's conducting properties will be the same a million years from now.