How old? Usually delamination is a manufacturing fault. That's supposing you haven't allowed the back cover to come into contact with any chemical agent. Saying that, I had a Samsung case that started to delaminate after 6 months and Samsung refused to help, but that was only because it was purchased thru Amazon (who glady refunded).
One thing to check is are you sure there isn't a seperate laminated cover on the back(like a protective layer), that's just starting to peel off.