I believe the real issue is how fit you are. Every year a dozen or so folk die from snow shoveling in Wisconsin. No one would consider snow shoveling an especially dangerous activity, but when coupled with sendentary life styles and lack of fitness, it can be deadly.
It has taken me about two years to be fit enough to ride 100 miles. My guess is that anyone that is injured in a century (not including crashes) has not adequately prepared their bodies for the event. I'm 58 years old and I know my limitations. I eat well and ride daily, but I am not ready for the 200km or 300km events that are tossed about on this forum.