Your story is so similar to mine it's strange. I took up cycling about 11 months ago after a 15-year hiatus. I rode my first century about a month ago. Not as fast as yours - - about 15.5 mph. I, too, felt probably my best at about 80-90 miles. I was a bit worried about being on the saddle for such a long time, but I thoroughly enjoyed it. To me, riding a century is like a rite of passage for cyclists. Way to go, and keep it up!