Figure 2. Percentage of adults aged 18 and over who met 2018 Physical Activity Guidelines for Americans for aerobic and muscle-strengthening activities, by sex and age: United States, 2020-CDC
Figure 4. Age-adjusted percentage of adults aged 18 and over who met 2018 Physical Activity Guidelines for Americans for aerobic and muscle-strengthening activities, by sex and family income as percentage of federal poverty level: United States, 2020-CDC
So, if you're an 80 year old guy showing up at the triathlon in the U.S., the odds that you are also quite affluent are extremely good. The interesting thing about the last chart is that there is no income level where the effect tops out. Since levels of smoking, obesity, and exercise were the factors most strongly associated with this trend in the associated study, it would also be reasonable to posit that the final bars in the second chart could be broken into a similar continuously increasing range over income levels.
I posted some global charts in another thread (probably also arguing with you ) which came to a slightly different conclusion. The difference between men and women were highest at the lowest income level, where men have physically active jobs and women don't while neither have time/money for recreational exercise. Whereas at higher income levels, men and women are about equally physically active because its all recreational.
Triathlons and endurance sports are a "high-income" class on its own because it requires setting ~2-3 hours daily for long runs, rides, ... it's a time-expensive hobby.
https://www.thelancet.com/journals/langlo/article/PIIS2214-109X(18)30357-7/fulltext#%20 wrote:Prevalence [of insufficient physical activity] in 2016 was more than twice as high in high-income countries (36·8%, 35·0–38·0) as in low-income countries (16·2%, 14·2–17·9), and insufficient activity has increased in high-income countries over time (31·6%, 27·1–37·2, in 2001).