I reckon reaching a target of a hundred, or any distance, can be achieved more easily than many people think - by getting your pacing right.It's funny you should mention that. Yesterday I was starting to think about wether or not I could tackle the magic century. As time goes by I'm sure curiousty will get the better of me and will have a go at it. It's going to a long way off though before I get to that stage, but it's going to be good fun training for it :-)
A lot of people push their rides, and end up with aching legs, sore knees, or whatever, and feel (probably quite rightly) that to reach a greater distance at the same pace will require more training, better fitness, stronger legs...
But, on the other hand, if you go at a slower pace that does not push your legs past what they can continuously achieve aerobically, and keep the fuel and water intake going at the same rate it's being used up, it then only becomes a matter of time - and there's no reason why you can't keep going all day.
At least, that's my theory, and it's my approach to the 100-mile I'll be doing in a little over a month. My rides so far have only been in the 40-50 mile range (although mostly off-road and so more demanding than road miles), but the key thing is I've been going at a pace that doesn't tire out my legs - I go for a walk afterwards as a 'warm-down' and a short ride the next day, and my legs don't feel like they're anywhere near their limit. (I'm also doing shorter harder-pushing rides, so I'm gradually getting my comfortable pace up a little too).
So when I do my 100, I'll be finishing way behind the faster riders - but I've got all day, I'll have a bag stuffed full of high-carb goodies (and sausages) and I'm confident I'll manage it.
Alan