I smoked for 35 years, quitting at age 49. I'd started cycling earlier in that year and gave up smoking because it was the first thing in my life that smoking interfered with that I preferred to smoking.

Twenty-eight months after taking up cycling, 21 months after quitting smoking, I travelled to Colorado. The very first mountain I climbed was Mt Evans, which at 14,160 feet (to the parking lot, 14,230 to the summit) is the highest paved road in North America. I suffered mightily on that climb, but I think it was more because I'm a lifelong lowlander and flatlander. Still, I did it, without extra O2, which I'd considered. At the time they'd begun selling little O2 canisters for cyclists. Those things have disappeared, I think.

In any event, it's hard to tease out how much was due to training and overall aerobic capacity (which includes cardiovascular) and how much was just lung capacity. If pressed, I'd say only 5% to 10% was lungs. You can't undo the damage done, only improve undamaged portions, and after 35 years, there’s little of that.

These days I can get individual rides to average 17-18.5 on the flats, but my overall average of all rides remains stubbornly in the 15s. Average speed of all rides in the year:

2006 13.82
2007 14.50
2008 15.25
2009 15.71
2010 15.73
2011 15.72
2012 15.66
2013 15.66
2014 15.65 YTD

If I were to cherry-pick, I can show numbers a bit higher than that. For instance, for all 95 rides YTD in 2014 on my Litespeed, the average is 16.44.

I'm also guessing that if I were to work a for-real training program I could improve the figure. I just don't have the temperament to follow a formal training program. Nor the interest either. Maybe those are the same things.

YMMV, of course. Me? I've simply decided to accept the consequences of my past and be grateful for what I have left. As it is I'm healthier than most 20-year-olds, and even my doc is jealous. That's good enough for me.