Volo-I too used to do the double birthday deal in my 50's but lately I've just been satisfied with a good ride of substantially less mileage than that. I just wasn't enjoying it as much as figured "Been there done that enough". To keep the interest level up I find that I need to do ride different route and go to different venues.......go to places I haven't been before. One year I even took the motivation to an extreme and bought a new bike that helped with the enthusiasm immensely.

I can't explain what caused you to lose "energy" on the August ride. I had it happen on a 100+ miler in December and it was all I could do to get back to the house. I too had eaten plenty and I thought I had drank plenty but for whatever reason I just didn't have it that day. I assume that we all have days that are not great on the bike. I don't have answers you are looking for. Just keep up the riding and you'll figure out what works best for you.