Originally Posted by
InTheRain
Don't you think most people that have been reasonably active throughout their lives could do a century without a whole lot of training?
Not without injuring themselves, no.
Not that a century is super-difficult; I find they're easier than, say, doing a half-marathon. But 8+ hours of repetitive physical activity, even low-impact, puts a tremendous strain on the body. Hydration, nutrition and fit are a big part of successful longer rides but not the whole deal.
It sounds to me like you were lucky or happen to have a rather resilient physiology. I think you are asking for trouble if you plan to do a double century and are inadequately trained.