> how my cumulative health decisions have depleted my energy reserves
I wonder about this too. Goodness knows that sleeping for ~4 hours or pulling all-nighters, eating the cheapest things on the shelf, and not getting in much physical activity late in high school and through college weren't sound decisions and are likely to haunt me for the rest of my days.
> if being lower on the Dunning-Kruger curve had some distinct advantages earlier in life (i.e. I expect things to be harder now which adds an additional mental obstacle and fatigue)
This isn't that much of a problem for me. In fact when it turns out that things put up less resistance than expected it's kind of refreshing and helps pull me along. The trick is getting to that point in the first place.
> What about you? Any specific things you think you could incontrovertibly do better in your youth that aren't likely confounded by other variables?
Hard to answer, really. Maybe sitting down and getting lost in the process of doing something creative… it came extremely naturally to me in my teens and early 20s but there are so background processes associated with being a responsible somewhat functioning adult running in my head now that it's considerably more difficult. Probably fixed by removing the need for those background processes to run, but that's not exactly practical.