This is a general question, but first a statement. Often, the physiology journals report of 12-week training periods with reports of X% improvement compared to the control group. Two years ago, I rode the same century as 5 years previously in 1.5 hours less time. I prepared for this century with much more early season leisurely riding. I would really like to do a 300 K or double century without being "wiped out" for the rest of the summer. How much improvement is realistic for me, a 60-year-old male; a person who only began cycling less than 10 years ago?