What age constitutes "old"?

[Lemur]

I hit the big four-oh this year, and came face-to-face with the realization that there are probably fewer years ahead than there are behind. But that doesn't make me feel old, per se. I think the other posters are right, you're asking two questions:

1. When do you stop feeling like a youngster?
2. When do you start to feel old?

I stopped feeling like a youngster when I took my first full-time job that didn't end when school starts. And I only feel old when I've been up all night with sick kids, as I was last night. But that's a temporary thing.