Despite years of conventional wisdom to the contrary, ropes age from use, not from sitting on a shelf.  The article below by Pit Schubert summarizes 17 years of European data. In that time, no accidents were the result of rope age, but due to falls on sharp rocks, and exposure to sulfuric acid.  He reports that ropes of 15, 25 and even 30 years old  "broke in tests accordance with the standard; they still held at least one drop; this means they will not break in practice, unless loaded over a sharp edge, in which case they may break".

At the time of this article (March 2000), Pit Schubert was the President of the UIAA Safety Commission, the German National Delegate, the Technical Director for the German Language, and chief of the Department for Research Safety of the Deutscher Alpenverein DAV (German Alpine Club).  He was one of the first Germans to scale the three classic big North faces of the Alps, the Eiger, Matterhorn and Grand Jorasses, and his climbing career includes almost fifty first ascents in the Alps, as well as several first ascents in Greenland and the Himalayas.