I now ride three days a week with one day a combo of interval and fast for 16 or 25 miles. One day recovery at 16 miles and one day (weekend) endurance at 50+. The rest days make a huge difference at 58 YO. I usually ride alone. My interval/fast days are on a MUP (off peak use times) though the 24 slow down, crossings, stops and other pace breaking interludes means that averaging 15 is my usual target. I pace the endurance distances on the highway at 15-16. I'm 5-10 @ 194 but I still have 20 to lose. My goal in the next year is a 17-18 mph average on endurance rides. Just losing 20 has made hills easier and losing 20+ more will be more fun. My ultimate goal at 60 YO is to ride at 190-200 watts steady and do the STP solo one day in under 13-14 hours.