Some habits are hard to break. I’ve been chasing personal bests all my cycling life but will be 78 in two months and find I just don’t want to work that hard anymore. My VO2max is pretty good, in the 90th-95th percentile according to Garmin and other sources, and I could go harder on my workouts but don’t have the motivation to do so (and I feel guilty about that.) I want to ride as long as I’m able and can comfortably ride 80-100 miles at 14-16 mph depending on the climbs and I think I need to follow a program that will help maintain my fitness when my goal is just that, maintenance, rather than improvement. I’ve used TR in the past and have long been a subscriber to The Sufferfest, now Wahoo Systm, and need some advice on the kind of program I should follow. Clearly, I’m interested in advice on TR plans.
Just wanted to say you are a badass! Stay strong and healthy. 
You have 4 years on me. I do find motivation is an up and down thing as is feeling guilty about blowing off workouts. Good luck in finding that happy medium. 100 miles every birthday is my goal. 100 when I turn 100.
Hey there and welcome to the TR community!
If you’re looking for less intensity, you might be interested in TR Masters Plans. Those plans prioritize recovery while still giving you 2 higher-intensity workouts per week.
Polarized Plans also feature less intensity than “standard” plans.
You could also look into our Traditional Base plans, which feature only Z2/Endurance riding.
Any of those approaches should help you stay fit so that riding long distances at a solid pace would be a realistic and achievable goal. 
Hope that helps – feel free to let me know if you have any additional questions!