I didn't consider making a baby adulthood, or getting a $100k/year job to be adulthood. If anything, I was _less_ responsible for my own actions (ballooning to 360lbs), because I started focusing on the things I _had_ to do, and let my personal development stop due to not having time.
Oddly, I realized and _grasped_ the concept that I had to take responsibility for my actions at around 19. But thinking that I had to check these checkboxes off my "Steps to Adulthood" list, I put off everything else in order to achieve it. I didn't actually achieve adulthood from that path, I just had the trappings and appearance of adulthood. But I was still about 13 years old inside.
I didn't consider myself an adult until the second time I made a judge run out of the courtroom (I declared a de jure court mid-sentencing after serving him notice of that right). The actual reason is less than relevant, but it was the taking control of my potential, and using it responsibly to help someone else, that brought me to adulthood.