There is so much out there to know and experience and it makes me sad to realise that there is no way that I'm going to be able to do everything.
I've a history of every couple of years diving deep into an interest. Woodwork was a thing for a few years, then wood turning. Gardening has come and gone a few times.
We spend a lot of time travelling and seeing new areas, slowly in a caravan, we never get to see it all.
Recently I've started running a Dungeons and Dragons game for a couple of my kids and their friends, there can be a lot more depth to that than you may think.
I've got to agree with you that you start to see a lot more things that you are familiar with. This is not really surprising if you are staying in the same environment.
Cycles of initiatives at work seem to come back every 5 or 6 years and they always ignore the same problems... sigh. There is truth in the idea that history repeats and the more things change the more they stay the same.
My suggestion for dealing with the feeling that nothing is new is much the same as everybody. If your world is getting boring and feels like everything is just on repeat, just change your world. Even if that means you are stepping into the unknown or you are taking risks, you are still going to change your experience.
This rings truer to me than anything else posted here. I feel exactly the same way right now, (in my late thirties) as if I suddenly realize I spent my life going deep rather than broad and that there’s a whole world of opportunities out there to be a beginner again, with the same enthusiasm as a much younger person (but now with resources!). The struggle of trying new things has completely changed my outlook.
My advice: try things you thought looked interesting but never thought you’d be good at.
So while something can be new, as one ages even "new" things have elements that are immediately obviously the same as one's past experiences. The older one is, the more of these elements there are. There's a diminishing return, so to speak, in experiencing new things.
If you can build a life around mastering Jiu-Jitsu or learning machining techniques, more power to you.
I'm 47 and in the same place. I have only recently come to grips with the fact that I am a good programmer and I do know what I'm talking about, but there's also so much that I still don't know. I keep learning, but you've got to pick your focus, because you can't possibly learn everything.
At 44 I have the opposite problem. The more I learn, the more I realize I don't know. When I was younger I had the ego of a young person and thought I was always on the cusp of knowing it all. As I got older I realized I was simply unaware. It's a bit cliché, but I started approaching everything, even things I 'knew' with a beginners mindset.
One of activities that really helped trigger this shift was finding something brand new to me at ~40 that I also became passionate about. In my case it was jiu-jitsu, but it can be anything where you're drinking from the firehose again. That mindset spread through everything else in my life.