I know you're not asking for advice but I feel like giving it anyway; You're a smart guy, don't feel like you have to suffer through crappy job shifts for the sake of being an adult. Do what you really want, because thats not the impression i'm getting. Life is too short to be unhappy.
And I agree with BC's view of adulthood. I don't think its a single moment where you say "I can finally make big boy decisions", but instead a culmination of life experiences that teach you to approach problems in a mature way without realizing it. Sort of like when you become good at a sport, you don't have to think about about how to move or act, because being adept just becomes a part of you.
I've always felt that, in a societal sense, knowing when you're "an adult" is harder for a man than a woman. Whereas women can birth children, for men this point of maturation is more blurry. We've also still got the expectations of being major providers in a family. This is something that I think has frustrated men for eons.