One thing I do know about being an adult is that it involves being responsible. Lots of days, I feel like I don't really have my life together, so how can I possibly qualify as a grown-up? Then I remind myself that a) many people - including people much older than me - don't have their lives "together" in terms of knowing what their ideal career is and b) I do my best to behave responsibly by paying my bills on time and keeping my apartment relatively clean and trying not to run my car into the ground and caring for my plants and pet.
One of my coworkers (who is 26 or 27) will be taking guardianship of her 12-year-old cousin in a couple weeks because of a bad family situation. The boy's mom died recently, and his father has been... acting out, for lack of a better word - staying out all night, forgetting to buy food, forgetting to take his son to school, dating inappropriate women (inappropriate in that the ladies don't call him out on his BS in not caring for his kid). She's a little freaked out. At the same time, she knows it'll be better for him than living with his father right now. And she's planning to take a new job that will let her work "normal" 9-5 hours. She'll be missed by us (I'll definitely miss her!), but this job is better for her career-wise, and certainly better for someone who has a pre-teen kid.
So, while I would be more terrified than my coworker at suddenly finding myself taking care of a human child, it has helped me realize that, in the essential things, I'm doing a pretty good job at being a real adult. I recognize when things depend on me, and I get things done in an appropriate time to take care of stuff. It's a reassuring thought that, should a crisis suddenly arise, I have the skills and coping mechanisms (and a pretty great social support network to call on!) to deal with it. So I guess I actually am a fully-functional adult? Such a weird thought.