I’m no pro runner, biker, or weight lifter, but at 63 years old, I exercise because of the benefits, not because I like it.
I do all 3 of the above mentioned, but mostly biking and weight lifting.
Once a person crosses the 40 year old mark, many things start to deteriorate, sometimes pretty quickly, like testosterone, HGH (human growth hormone) and many other functions such as the immune system getting a bit worn out.
Exercising can help combat al this, and even if it’s just a few days a week at about 30 minutes each time, it can make an amazing difference.
And yes, the “use it or lose it” really applies here.