I hold read about people keeping blind parrots. I intuitively don't see how being blind could affect their age (unless of course its a flighted bird, which could potentially be a problem.)
Some people would hold ditched the blind bird a while ago, but Im sure you love your bird and your bird loves you. That's all that really matters.
Answers: I think it's great that you are willing to care for a disabled bird. So copious end up in shelters. I'm sure you've get good vet care for him and already have his coop set up so he can easily maneuver about. Keep his wings clipped so he can't hurt himself by flying unchecked. With a healthy diet and lots of love and attention from you, I'm sure he will live a happy existence. Hard to say how long that will be without knowing what kind of bird he is, but as long as he have no other health problems, I'm sure he'll live as long as other birds of the same breed.
If it can feed and drink ok and doesn't have any other problems, he should live a normallife:)
Your bird should live as long as any other bird within its species as long as it doesn't suffer from any other disabilities or diseases. You just have to be careful near it.