Having seen this thread many times before.....I skipped all the replies.
Reference: 70yo, 35 year road cyclist, No medications,
100mi/wk, 7-8mo/year has been the goal lately, usually achieved.
150mi/wk - when younger - often missed when kids were young.
Question: How to train?
Answer: It depends.
What is your medical history + current condition?
What are you training for?
If training for a competitive goal or timed century or Masters Olympics - then you have need for a structured program that will include intensity. How much? Depends?
If training to substantially lose weight, lower blood pressure, overcome Type2 diabetes, etc - a structured program should greatly help. Intensity? Depends?
If training to maintain one's health and feel as good as possible each morning/noon/night - well maybe, Listen to the Body, Move, Smile.
Cardio+Strength =
Lots of branches on that tree of Intensity.
Personally, gardening a 1acre property bordered by forest 180° - by hand - is a combo of stretching, yoga, tai-chi, hand strengthening, and other stuff. Oh yeah, hiking in that forest mostly fills in a lot of the non-cycling months, now that I ski less.
edit: Clear your handlebars and your mind will follow.