I've got lots of music on CD-R's that are more than ten years old and they all still play fine. As long as you keep them in their cases when they're not being used, and store them away from sources of heat, moisture, etc. they can last quite a long time.
Thanks Freddy, but my stock of re-writable and write only CD's are still in the original wrapping and untouched for over ten years. I am wondering if the actual lifespan will begin after I start using them if I ever think of using them!