Same.

I find the physical struggle invigorating.

I see a lot of headlines about having more muscle mass keeps you more able and healthy over your entire life.

I also see a lot of inspiring videos of 70, 80, 90 year old people ( including women ) looking very athletic or lifting large weights. Even more inspiring is that someone of them only started training a few years ago. Some of the people in those videos could pass for being in their 50s if they colored their hair.

When I was a teenager I read an autobiography by the man who brought karate to the west after WWII. He lived to a very ripe old age. He wrote that people were surprised he could get up and down his stairs, walk about town, without assistance.

That seemed silly to me at the time, but now I am seeing people I know who don't workout that much get decrepit. I have some joint damage that no doubt would be much worse if I didn't exercise.

Having strength and muscle later in life IS an investment like you wrote. It helps guarantee independence and that you will be more functional.