If it helps at all, you are not alone in this. I’m probably a bit older since I’m already at the retirement planning stage, but I feel the same about the lost opportunities thanks to circumstances (some my own making, but most just because of life). I’m just hoping that I can retire early and recapture a percentage of what I used to have in enjoyment, learning, and creativity while I have some of my brain left. Right now I have rare fleeting sparks, but usually I’m just too tired.

And that last line… realistically almost all people that have lived have experienced lives rich with experiences, good and bad, all lost to time, but it’s still tough to understand that from your own pov. Cue Pink Floyd’s “Time”. Try to enjoy what you can of the now.