You will do fine. You certainly have enough base miles in your training. The mileage will go a little faster and easier as it will be an organized ride and there will be others out there.
Eat before you're hungry and drink before you're thirsty-in fact eat and drink by the clock rather than how you're feeling. Go easier the first 50-70 and hang on wheels EVERY chance you get.
However, do plan to be "challenged" by the last 20-30 miles. It's as much a mental challenge as a physical one. Take breaks but don't hang around the stops too long. Ride "point to point"-ie, go from rest stop to rest stop or even set your goals to go 5 or 10 mile intervals and reward yourself after hitting that mark-even if it's just with telling yourself "Great job Alabama Man!! You can do this!"
Get to the end any darn way you can-just keep the bike moving forward-speed is not the issue. Your plan is to finish. The reward of doing number 1 is just an incredible feeling of accomplishment by breaking a barrier you don't know if it's one that you can really do.
Remember the 50+er's are behind you 100%!!