I just finished my first century with 2900 feet elevation (thankfully, one of the flatter centuries because my legs have been exhausted for 3 days). I was able to average 16.6mph because some really nice strangers let me draft behind them (I always ask and not just draft randomly because I am wobbly when I ride and I want to make sure that the rider in front of me knows to signal/warn me of obstacles ahead).

My advice for a first century is to stop and fill up your water bottles with gatorade and grab a snack to put in your jersey and pee at every rest stop so that you are as comfortable as possible to finish....at least, that was what I did. I also did take 1 Tylenol at the start of the race to try and prevent any aches/pains that was coming.

Most of all, I try to finish without injury/getting lost. Some of the riders that I know were lost for 10miles. So, watch the holes/the road cracks/being too close to the gutter/cars.