NB Regarding the "fumbling through" feeling, I'm 53 and I think one of the comforting things about getting older is realising that it's not just you but that, in general, everyone is pretty much making life up as they go along :-)
This has also been my observation at 30. I've worked with people all ages and people of all statures and most people are just doing what they think is right and not much is based on facts. Even high ranking people at fortune 500 companies are just doing what feels right to them and often their success is more related to people below them working their asses off than their leadership. The only difference between people who are in control and people who don't, is often that the former don't have a realistic view of why they're successful.
And, as a nuance, there are of course people who are really good at what they do and that have a lot of knowledge. A lot of people, however, just were really lucky (or really good at networking) to get where they are. Even some Nobel Prize winners just got lucky: