What's weird to me is that I never felt that transition happen. It just seems to have occurred over the last few years. A younger me had a real hard time saying no, now it's easy and liberating! I can't tell if it's an age thing or something else though.
I don't think I can transmit this feeling by explaining it, since it's something you can only decide for yourself, but I made the choice to focus on the positive. I still keep the cynical realness in the back of my mind, should I need it, but I don't want to spend most of my time there anymore.
It's been over a month now of much improved mood, hopefully this will stick.
If you're interested I'd recommend reading Thic Naht Hahn, Tolle, the Bhagavad Gita (get it with explanations, The Essence Of is great), etc.
I've found that whether or not I practice the teachings just continuing to read about them keeps me mindful.
And daily metta meditation.
Granted I have far more responsibility than when I was in my 20's, so I think it it's basically a wash there, but at least I'm not stressing about things that seemed really important over a decade ago.
To me it's a source of content and acceptance but depending on your personality it can go the other way.
I still have things I want to do but if they don't happen I am OK with that.
I think it's perfectly fine to be content with this perspective.
However, just a note that many, many people and figures past and present fell into their zone for the first time even in their 60s.
For example: I would love to run my own small company. But I have learned repeatedly that I am no good at selling and also not very creative in coming up with new products. So now I am content with a regular job.
That combined with being able to sift through the shit storm that life throws at you, for the ideals you want and ignoring the rest, helps a lot.
And later you realize you just have this amount of “worries” left. So you better spend them wisely. ;)