Ditto the other replies.

I rode the Greater Cincinnati Tour De Cure 100k in the spring. It was my first long distance event, and I had a great experience. I am 49 and had been riding about a year when I participated. Try to find someone with whom to ride, as it will make the trip much more enjoyable. If you don't know anyone who can go with you, there should be no problem meeting folks there of a comparable fitness level who would also welcome the company.

Additionally, there should be 3 or 4 stops along the way with drinks and food. I would expect you could check with the local ADA for exact information. Drink plenty of liquids, eat and have fun.

The ADA does a great job supporting the riders. In addition to supporting a great cause, it will be very satisfying to get your first metric century under your belt. I don't know what the terrain is where you are, but if it is hilly, plan on being exhausted by the end, but persevere. You can do it.