If I may be serious for a moment: I see posts like this fairly regularly, and I fully believe that they are true in some broad sense. But my thirties have been entirely defined by one thing and one thing only: COVID-19. I feel like I missed opportunities to live my life before age 30 not because of some abstract fear of aging, but because I have literally been forbidden to live my life in my 30s beyond the bounds of my home. A deadly virus, a malicious government, and a sociocultural milieu that falls somewhere between "blithely uninterested in keeping people safe" and "baldly eugenicist" have come together to create a context in which I rarely get to see my friends at all. When I hear from them over the internet, as is the only option, I'm constantly afraid it's going to be news that yet another has developed an incurable chronic illness.
So I guess I'm lamenting not only that I didn't do more in my 20s but that I don't get to have this transformative experience of coming into my own as a person in my 30s. In a way, time stopped when I was 29 and, given the utter lack of effort going into making it possible to live safely in a world with COVID-19 in the long-term, it may not start up again until I'm approaching my 40s.