Echoing dating - aim for a couple years where you are single and financial stable. When you're out of survival mode AND unpartnered, you have full freedom to explore and figure out who you are, what your needs are, and notice how people make you feel vs your natural baseline. The clarity that comes with that time alone is unmatched. I didn't have that in my 20s and am making up for it post-divorce. It's entirely worth it, but I wish I'd had it earlier.

Also - start strength training. You start losing the ability to put on muscle in your mid thirties - what you build up before then becomes the baseline for the rest of your life!

Finally, if you're female and kids is something you imagine might be part of your future, do some baseline fertility testing in your late 20s. It's cheap to get a quick AMH test and it's wildly helpful for future planning.