I'm sorry I don't really have a lot to offer with regard to your concern. However I noticed you had yet to receive replies to this post. So I thought I would write one.

I myself am an "adult" too many times over. No one really ever taught me how to do it either. I learned as I went along. (I'm still learning.) I think a lot of us do it that way... sink-or-swim... trial-&-error. Admittedly it's not the best way to do it. But it's the way it was (is) for many of us.

Here are links to 2 articles, from PC's archives, on the subject of "adulting". The first article is targeted at parents. However it may still be of some interest to you; plus both the first & the second articles provide links to & / or information on additional resources. The third link is to a Psych Central podcast on the subject of adulting:

Preparing Youth for a Smooth Transition into Adulthood

Are You Ready to 'Adult'?

Podcast: How to Make the Transition to Adulthood Easier