Mine was in spring of 1973. A group of us had decided that we were going to do a bike tour during our spring break. My longest ride previously had been back to back 60 milers. First day of the tour was 105 miles. It was in late march in Southern Illinois, s there had not been much time for training. As I recall that day was SO long. But we made camp by nightfall. That day was followed by 7 more days of 100 mile plus rides on fully loaded touring bikes. We lost a few guys along the way, but six of us finished the tour. We ate fast food and grocery store crap. At that point I realized that a century was not really that big of deal, just a long day in the saddle.