You do not have to do 100 miles training to prepare for a 100 mile ride. Those trips up your mountain a few times were good enough. Bonking and the danger point is 70 to 80 miles so you caught it in time. 100 mile rides and I make my one stop- other than for water- at around the 65 mile mark. I eat on the ride but at 65 I eat something a bit more substantial- drink a full bottle of water and stretch a bit, No more than 5 minutes and I keep moving at that stop.

I would love to do 100 miles in 8 hours. I have done it but think I would be taking longer now. Lack of training and enthusiasm would slow me down so well done on the ride- the time and your attitude for the next ride.