I experienced just the opposite in regard to albino's. Albino's were my first cory's and they expired about a month after I got them. I figured it was due to having put them into an immature tank. I asked around and got some better information:
Cory's, like most other bottom dweller's, will be in contact with the worst of the tanks parameters on a consistent basis. A lack of supplemental foods will also cause problems. Having them in insufficient amounts can also be at issue.