Besides the above, with which I agree, small portions. 70 now, but down to the weight at which I climbed when I was 21, plus I'm stronger. A very good book outlining the principles of weight training and keeping the weight off is Body by Design. I don't follow it exactly because I don't eat meat, but I use the principles therein. I avoid eating a larger dinner by having 25g flavored whey protein in water when I'm starting to get hungry at bedtime. I have a healthy snack ~3:30 in the afternoon. That keeps my lunch and dinner size down. A favorite snack is a jigger of virgin olive oil and a handful of walnuts. I have a list of maybe a dozen snacks I rotate through. A lot of it is simply getting your stomach and body used to eating less.

I get a heck of a lot more aerobic exercise than in the Gethin book, total volume 8-15 hours/week depending on the season. Three of those hours are lifting in the gym. I always ride my rollers for an hour immediately before going to the gym. I try to lift to failure on the last set of every exercise. That's how you get strong while staying light.

On the bike, I use polarized training, see:
http://www.bikeforums.net/road-cycli...l#post18411538
https://www.antoniocgomes.com/wp-con...e-enduran1.pdf
Polarized training has greater impact on key endurance variables than threshold, high intensity, or high volume training