I'm the luckiest SOB who ever lived. I met the person who would become most of that 53 years go and married her. She's not my trainer though. I do have a personal trainer, about 3" behind my eyes. He uses TrainingPeaks and is a hard taskmaster. At the end of every week TP generates a number which is my current fitness to ride. And there it is in black and white, how hard I worked or how lazy and foolish I have been. IME it's quite accurate. If it's 30, I can ride 20 miles no problem. If it's 80, I can ride 200 miles no problem. Seems sometimes like it's just ego, but OTOH it's also long life and happiness. Maybe nothing's all that bad about ego.

Musing about more of the above comments . . . Light bike doesn't make much difference IME. I can gain or lose 2 lbs. quite quickly and don't really notice it. Of course 10 lbs. is another matter, but I assume that 25 lb. bikes are not what most of us ride. My single of choice is 2000 vintage, weighs about 18 lbs. but is stiff and goes where it's pointed. Don't notice any obvious disadvantage when riding with others. That's all about my fitness. We ride a 36 lb. tandem, but that's 18 lbs. a person, plus the team has maybe 25% less wind resistance than two people on singles. We rode RAMROD on it at a combined age of 135, finished inside the time limit.

I also have aero bars on the tandem and my single, makes a difference. I don't use them if there's a bike within 25' of my front wheel or when hard cornering. I am a bad boy though and will drop onto them when pulling. IMO the first bike should be all the way down, second bike almost down, 3rd bike on the hoods. I see so many pullers on the hoods, slows the whole paceline. Yeah, we all got our personal little gripes.