I'd been riding for 8 months when I did my first century. I'm a textbook example of what NOT to do before your first century.
I hadn't ridden much the two months prior to the century itself, but I rode 57 miles the day before the century and drank three beers the night before the century. Century day was upwards of 95 degrees with 95% humidity and I thought I was going to DIE. Didn't eat or drink nearly enough, bonked at mile 80, and suffered half the night afterward (puking, couldn't eat, etc). Took me almost 8 hrs of riding time and 11 hrs total time to finish that ride. I learned a lot from that experience, but was kind of afraid of long rides after that.
Seven months later I decided to attempt my second century. I had been training a little more but didn't overdo it in the days leading up to the ride; the weather was nice and cool, and I took in plenty of electrolytes and food enroute. In spite of 20 mph headwinds for the last 35 miles, I finished in 7 hrs riding time, 8 hrs total time, and had energy to spare at the end.
Advice? Hydrate and eat properly and don't do what I did !!

