Looking at all these replies, it seems pretty simple:

The good old days were good because it was a young person who was living in them.

Is this a simple physical process? Is it more about the naivete versus the experience? Does cynicism grow on you along with the normal survival tools?

You know, if anyone ever does live to be 300 years old in the future, we would learn a lot by what their eventual attitudes turned out to be. I couldn't even guess.

I watched a TV show once based on the movie "Highlander." In the series (I never saw more than a few shows) there are apparently more immortals than you can shake a stick at. But most are in their hundreds, and lucky to make that since they seem to be in the habit of killing each other off (how's THAT for an evolutionary dead end?). But there's was a guy in this show from ancient Greece or something who was thousands of years old. A more laid-back view of life you'd never seen. I guess when you've lived that long you might realize that "this too shall pass" applies to almost everything.