Good for you for putting your exercise and fitness rergimen to a higher cause. Each year I ride a century ride in support of Juvenile diabetes, as my 15 YO son is a Type 1 diabetic. This will be my 6th century ride this year, and I assistant coach the Minnesota team.
Soooooo, why not the century?? how far and how often have you been riding? Looks like you have 2 months left to train to get ready. One thing to remember, you will be able to go 20% to 40% further on ride day than your longest training ride, (weather and hilly courses not withstanding) just because of the adrenalin high and the cheering and support of the crowd. We have had new riders train for 1 summer, and ride the century after riding training rides up to about 75 miles. We start off in the Spring with slow paced rides of around 20-25 miles and increase the mileage 10% per week till we hit around 80 miles. We also encourage team members to ride a couple of "short" rides on their own every week.
Have fun, ride safe and keep smiling!
Cleverly disguised as a responsible adult.