Answer
"MAM-A estimates their Gold label CD-R's have a life-span of 300 years and the silver CD-R's of about 50 years. Other discs that they have tested look like they'll fail in 2 years or less.
Due to differences in organic dyes between CDs and DVD's, Gold label DVD's have a lab-rated life-span of 100 years, if handled properly. MAM-A silver label CDs and DVD's can start to degrade after 20-30 years."
Source:
http://www.larryjordan.biz/articles/lj_dvd_life.html