depends. Some low-quality cd-r media s are only good for a couple years (3-10) average. Cheap media use dyes that degrade fairly quickly. High-quality (archival quality) media are rated for ~50-100 years mean lifespan. More likely than not, you don't have archival quality cds, and some of them may be degrading.

Legitimate, stamped cds and dvds are rated at ~100+ years, regardless, because they use a different process than burned stuff that doesn't rely on photosensitive dyes to store the data.

You might want to pick up a lens cleaner for your player, or it could be the player itself degrading. Have you tried on a different player?