I play music with a lot of old hippies (55-75, which to me isn't truly decrepitly old, but I'm 36 so these aren't folks I consider to be "my" age group). I gave up smoking about the time I turned 30.

The guys who smoke don't seem any less sharp than the other folks I know in those age groups, and they seem on par with the other folks I know of all age groups when they are smoking. So yah, I know plenty of wise old guys who regularly smoke.