One piece of evidence supports this theory. People who are obese (30+ BMI) between age 25 and 40 lose from one to six years of life, on average. It doesn’t help increase lifespan to lose weight later in life.
I know that exercise helps lower heart rate. Because I’m a pilot and see my heart rate records going back to 1964, I know that my five days a week of running for three years lowered my heart rate by 15 beats per minute, average, and my continued running kept it low since then.
I got the fifteen beat reduction which comes to 8 million extra beats per year by increasing my heart rate for an hour a day by 100 beats per minute. The exercise took an extra 1.5 million beats per year off my life long heart beat total but generated 8 million more heart beats by lowering the average for a net gain of 6.5 million beat per year.
Exercise probably helps longevity. I will have have an average of 325 million extra heart beats during my life because of exercise for a 12% increase in my lifespan.