...im a bioscientist. I know my fair share about the human body and all those 80y old marathon runners and bodybuilders are just natural human beings.

A true scientist does not ignore facts to force an argument to work. There are senior marathoners. There are also seniors who are bed ridden from health issues or in nursing homes because mentally they have broken down so much they can't remember who or where they are, and need other people to care for them. Plenty of those seniors aren't even much past the age of 60 yet.

Genetics. And to an extent, life choices, of course. But there are marathoners that die of heart attacks before reaching their senior years.

And being a marathoner doesn't inherently mean your life is good, either. You could be a marathoner because it helps you deal with other health issues... if you are young, do you need to run marathons to be healthy? Or does it just come naturally? The older we get, the more time we need to spend on maintaining ourselves in order to be healthy enough to still enjoy ourselves... but that time spent maintaining consumes more and more of our life until there isn't much room for simply enjoying anymore. That's the real quality of youth. It comes naturally. I remember what it was like to be young. Putting in effort didn't feel like effort because it was enjoyment in and of itself. I was lucky, because I know not everyone gets that. But I did. Now effort is to slow the descent. I do not enjoy it, I do it out of necessity. And the only fruit from it is tomorrow will not be as bad as it would've been if I had not put the effort in. That is not a harvest. That is slowing the decay.

And that is part of being a natural human being. It is not romantic in any way.