I am distance runner of 32 years and took up biking in addition to running more serious 2 years ago. My best marathon times were when I was 31 years old and the times started getting slower. I think long slow distance is probably making me good at long slow distance. My running times since I started riding about 2500 miles a year have been now better than a few years ago and I am 49. I don't have any real speed but could still run a marathon well enough it has been 10 years since the last one.

Now on the bike I have really improved this year but I can tell I am reaching my limit unless I stop running but I don't want to do that. I can see at this point my speed on the bike is limited by my age but also I am not too daring. I don't go around tight turns fast and hate riding faster if there is traffic. I think basically past 30-32 if you have done endurance sports for a few years you will go down hill slowly in speed but I still have endurance. I can go for a long time steady and a decent speed but need more recovery time.