While I might give the same advice of starting with the metric, if you train right and learn the road skills, you can do it. Set a realistic time expectation, learn how to drink and eat for long distances, and practice the hills.
I did my first century last fall. Although i have been riding for 6 years, I didn't really train for it, in the sense of doing a specific training plan. However, I chose a flat century for my first one. I knew I could do it, even though my longest ride previously was about 70 miles and it wasn't even during that season. In fact, I don't think I rode any rides longer than 55-60 miles last season, except for the century. But, I do ride hills all of the time and I think that prepared me for some of the difficult stretches we encountered, due to wind and a torrential rainstorm at about mile 85. A lot of the preparation was mental. I set a realistic time of 7 hours, slower than my normal average and was happy when I did it 6 hours, 35 minutes.