Well firstly your senses do start dulling (eyesight, hearing), and secondly you have way more context on the world itself (the mortgage bond, climate change, pollution, family responsibilities, social media trolls, the fragility of bones and life, etc). So I suppose your brain is less focussed on the moment, and you’ve got a bit cynical about life ;-)
I accept that the way I looked at life and moments at 15, 25 and 50 are fairly different. Decisions I took at 25 were right for me then, but today I would have decided differently, but then I would not be where I am today either.