I have read many times that people are happiest in their 70s, simply because they have zero f*cks left to give.

Free from the shackles of other people's expectations or worries about their judgement, most people make a sort of peace with themselves, accept that their looks (if they ever had them) are long gone (so no point worrying about it now), and just enjoy the experience of being. You don't have to work, you don't have to strive, you can just exist and potter about a bit, doing hobby stuff.

Even in my forties, there's much to envy.

What you do seem to need, to enjoy this carefree existence, is enough money - you don't have to be rich, just not-poor - and good physical health.

I'm warned time and time again that everything else is worthless without the latter, so I'm doing a bit more walking now, cutting down the alcohol, so that my senior years can be as fulfilling as your own.