I did my first century in 1988, a Thanksgiving weekend thing called The Tour de Turkey. I had done a 75 mile preparation ride a couple weeks prior, but I got pretty sick before the event. I struggled and coughed and whined my way through it, thinking I couldn't finish many times. I was coughing so much, some wise guy suggested I should quit smoking. After the ride I realized, beside the sickness, the mental barrier was the biggest thing, and my second century, while a harder route, was much more fun and I had a great time. I think I did about 50 rides of around 100 miles in 1990. Now, they kick my butt pretty good, but I still enjoy doing them.