By Mark Cramer, retiree, cycling advocate, regular contributor to  Freewheeling France   22 percent of the net growth in U.S. bike trips from 1995-2009 is by people ages 60-79. Their biking quadrupled in those 14 years, the fastest growth of any demographic. During the past 17 years I’ve been cycling on a regular basis. As I’ve aged (I’m 72 now), I have observed an increasing population of senior cyclers around me, especially in France, my home base. Recently in Paris I presented a slide show on Cycling in Bolivia. The canyon city of La Paz, Bolivia, where I live for six weeks each year, is 12,000 feet above sea level, has no bike lanes and if you find a rare flat street, it’s never going where you need it to. Given the challenge of cycling in an area with sometimes many thousand foot variations in altitude, I expected a younger crowd to attend the presentation. Instead, the audience was comprised mainly of seniors. Mingling with them I learned that their retirements are e