Depends on the medium. Old fashion paper based prints fade very quickly in light, newer RC much longer, Fuji claims 75 years for crystal archive. Cibracrome/Ilforicrome 40 years, dye transfer 75 years or longer. I still have color prints that my father took in the 50's that are holding up, and I have prints from the 60s and 70s that show no fading at all. My early cibracrome look as good at the day I printed them.

Regards

Paul