Get out this weekend and ride 75 miles with 9000" of climbing. This is 75% of your century distance and climbing. If you can finishh that training ride, you might have a fighting chance. 10,000'+ centuries are really tough (just did one with 12,000' in early May), I would suggest as other have, doing the 50 miler, or chosing a more reasonable first century. That being said, if you really want to, just go as far as you can, you can always get sagged in if you bit off too much. Good Luck, and give us a report if you try it. Also, if you do go for it, make sure you have correct gearing for that type of ride (at least a 39 x 27 or a triple or compact).