I'm 26 and still do. It doesn't bother me much, unless I was drinking and smoking like a demon the night before - but then it's a combo of hangover and smoking that slows me down.
But usually I'm fine, I can still go out there and play. I know long term it'll get to me, by the time I'm 31, 35, 40 or something.
I'm not saying to keep doing it, because that'd be stupid. I do think that it's overly thought of as real damaging if you smoke and try to play sports. I keep up just as well stamina wise with anyone, whether its hockey, baseball, paintball.
Just saying I'm sure it doesn't help. I'll quit soon enough, and have been skating more, rollerblading more in the summers to just keep it up.
And not to say "this NHLer did it" - but the first person I ever saw in my life chain smoke when I was a kid was Maurice Richard. He also drank a lot of beer, sure he was retired at the time - but I highly doubt these were habits he picked up after playing.