I've been reading lots of threads about preparing and training for a century. I don't consider myself to be really fit - I'm probably 50 - 70 lbs over ideal weight - and I was able to do a century without much trouble. In fact, the longest ride prior to my century was 50 miles. I completed the century by actually starting a 200 mile ride but with no real expectations to finish it. I just thought to myself that I would just go until I got really uncomfortable. That happened at the 125 mile mark, and I threw in the towel at the 140 mile mark.
Don't you think most people that have been reasonably active throughout their lives could do a century without a whole lot of training? If they have good equipment that fits right, I think most people with average fitness could push themselves to complete a slow century (10 hrs +?) I felt like my downfall on the 200 mile ride was my lack of knowledge concerning hydration and nutrition. I thought I had been drinking enough but it was apparent that I had not. My muscles began to cramp severely. However, the next day I felt fine. I was able to climb back on the bike and ride surprisingly well.
This year I will do the 200 mile ride again. I'm planning on using a camelback to insure that I drink often enough. I'm probably not that much more aerobically fit than I was last year (maybe that will change in a few months) but fitness wise I feel that I can complete a double.