I agree with the higher intensity and more rest. I'm 54 and started doing one full two years ago and doing my third in a few weeks. I used the 36 week tri-fuel program that I rewrite to fit me. It's written for a young, fast person with 15-20 hours of week to spend on training. But what I do like are the swim workouts(interval oriented) one run on the track per week, (intervals) and 1-2 bike workouts that are intervals, and the run and bike intervals take the place of longer runs and bikes. I mostly just use the 12 weeks of competition and 2 weeks of taper. My business is very busy until September and tapers to nothing that month and dead in October and November so this is the time I add hours to my week training. September goes from 6-7 hours first week to the last week around 12-13. October is 12-16 hours for four weeks and November has two weeks of taper. Two swims per week September to mid October than 3 after and November usually 4. Long bike in September is 60 miles then October has one long ride a week, 75, 90, 95 and 100. Long bike is usually outside and interval bikes are on a smart trainer or a gravel bike with an aerobar that I ride on limestone trails. For running, one track workout( I was a division 1 middle distance in college and love to get out on a track still) and then every other week I run long 12-15. Otherwise a 2-3 times 5-8 milers per week with varying speed during those runs, (usually try to negative split those runs). Take a look at that that program and how he writes the individual workouts and tailor it to you. I feel I know my body and recovery better than anyone else and I enjoy taking a program and tailoring it to fit me.