Well, Clinton DID age from 46-54 during his Presidency, those years start to show on everyone I've known. I'm sure the job had something to do with it, but it's hardly all.
I agree that Cheney won't and probably shouldn't run, but he's so calm and knowledgable, I don't think the job would kill him.
You're right about the age time frame. The best example is Carter, hell, he looks worse than Robert Redford and that was in 1980.