A very interesting question! One that I've pondered meself a time or two or three.
I used to be super-sharp- at least as far as actual, hands-on stick skills went. On the far side of 50 now and not flying nearly as much as when I was in my 30's and flying 700 hours/year, I wonder if I'm as good as I was? Am I at the top of my game? Or has the downward slide begun? I hardly ever do the things I used to do "for practice" anymore. And certainly my vision is hardly as sharp (damn bifocals). So does my accumulated experience make up for my reduced reflexes? My ego convinces me that I'm still razor-sharp, but still...how could it be possible?
There's no way that I could delude myself that I'm still "in my prime." I also commend "nosehair" for his candor. I know I'm still "good," but the fact is that I'm not a kid anymore. When I realize how much I've forgotten, or how much I have to go look up when someone asks me a question, the point gets driven home quite poignantly.
That pasture is looking awfully good...maybe it's time.