I haven’t been an adult for very long so I don’t have a ton of experience on the matter, but I do have a theory about adulthood.
It doesn’t exist.
No, there’s no such thing as an adult. When you were a kid, everyone you thought of as a grownup was actually just a slightly taller person flailing around and making stuff up as they went, hoping no one would notice. This theory terrifies and comforts me at exactly the same time.
Now I’m one of those people, so to help me make stuff up, I’ve been referring to an Ideal Adult who exists only inside my head. She makes good, grownup choices so I try to follow her lead. What would the Ideal Adult in your head do? is something I ask myself a lot.