If you were serious about going fast when you were under 45, and you are now in your 60s, you will never be able to match your speed when you were under 45. That is because between the age of 45 and 80, athletes lose half their capacity to extract oxygen from breathing, and nothing is going to make up for that. If you were not training as well or as hard as you could have been five or ten years ago and you are in your 60s, then sure, you could start training correctly and match your old speed from five years ago. And yes there is a correlation between being athletic when you are young and ending up with an irregular heartbeat when you are older. You can always learn to appreciate being able to ride more than when you were young though, but as usual people put speed as some sort of necessary thing to enjoying cycling or even life itself. You can tell by the way they drive to work in the morning..........