The only difference between successful adulting and being a kid is a self-discipline and fore thought. Also, the consequences for lack of self-discipline as an adult are usually disastrous. So, plan ahead and be conservative and be smart.
You're only now having to become "at least somewhat responsible"? Being "somewhat responsible" to the extent of my capabilities was ingrained into me by parents from as far back as I can remember, and kept increasing as I could handle more and become more independent and have a part-time job and not just an allowance. So it was never a big shock. I raised my kids the same way, and my grandkids have been raised the same. It's part of parenting -- nurturing, preparing, teaching self-sufficiency.
Adulting is hard, but it's got it's ups and downs. It was a huge up for me as an adult to realize. I make my own money and can buy my own groceries. It was a huge down to figure out why my parents never let me eat a gallon of ice cream for dinner. Still have to apologize to my gut for that one.