adulthood is a state of mind, not an age.
When you are responsible for your own living expenses, even living at home can be “adult”. It is the level you take for growth in your future.

I think being an adult has everything to do with maturity, not necessarily living on your own or having children, but these things would presumably make you mature.

when you stop believing in santa
I agree with @jazmina88 and @RedmannX5 , it is also always taking responsibility for your own actions, and being able to organize your own life with minimal help. (People always need help from others in one way or another no matter how grown up you are).

Losing optimism and seeing your shitty life for what it is. Lol. But I would also say taking responsibility for your actions, and paying your bills.

Being an adult does not mean losing or getting rid of the fun-loving child inside you, but embracing that kid, and knowing when to let that kid out.

@Blackberry I disagree, I feel much more optimistic now I am out of that high school crap and you realize that life in school is really enclosed and doesn’t mean anything. I now have tons of friends, recognized for my hard work and always chatted up and noticed for looking pretty but classy. I have gained optimism as I have grown up. As a child/teen I had no confidence, no freedom and would worry myself sick about everything . Now I have both and can see the bigger picture in life and so only worry about the things that matter. I also agree with @linguaphile . I am much happier as an adult.

I just had this conversation with my 18 year old son.
He is a senior in high school and was balking at some restrictions that I had given him.
He said (loudly) “I’m an adult and you are telling me when I have to be home?”
I said “no you are not an adult. You are an adult when you can be responsible for yourself, take care of yourself, and support yourself. You’re getting there but you aren’t there yet.” He didn’t argue, he accepted my terms and I believe that that is one more indication that he is on his way to becoming an adult.

You’re an adult when you can be trusted in a life or death circumstance. That could be when you’re 16, or it could be never.

I considered myself an adult when I left home at 17.

@bongo I agree. :)

I agree it is more of a “mature” mindset, and less about external accomplishment.
Being emotionally “mature,” walking your talk, keeping your word, following through with your obligations/commitments, being pro-active and not avoidant of problems, taking personal responsibility for ones words and actions, having the ability to be reasonable and see others POV’s and apologize or admit error.
Being able to take constructive criticism, feedback, without getting your ego all bent out of shape.
In other words, having integrity.

Theres a saying I have always liked that goes ” His body may have arrived at the head of the table, but his mind is still in the playpen.” lol

Sex.

@Luiveton How so? I think you’re saying responsible sex, but I just was curious.

When you can pay for yourself and aren’t depended on anybody else.

Shit man! I’ve been a dolt all my life. Can’t be much harder being an adult. I’ll let you know when I become one. Stay tuned.

There is a huge difference between being of legal age and being an adult. Some people attain adulthood very early in life, others reamain spoiled brats for decades.

I think adulthood comes in phases. First is the realization that the world doesn’t owe you diddly and you are responsible for your circumstances. While there are many things beyond yoru control, what will always remain in your control is the actions you take. For most, the first baby steps towards this are when they turn 18, go off to seek their fortune and realize just how much time/effort is involved in the basic tasks of living that most kids take for granted, then eventually figuring out that improving your lot in life takes real effort and mommy/daddy can’t make it magically happen for you.

So… you finally think you have arrived when you hit your later 20’s and believe you have your act together. Then sometime between then and your mid-30s for a good percentage of folks the first child arrives. Then you realize that all that work you did to get your act together as a young adult really only amounts to the basic intorductory course in adulthood. Now the real learning begins….

In humans, maturity does not set in until about age 25 in most people.

Wife and I are in our 60s and we still have not grown up.

Oh dear. I didn’t think I was grown up until I was around 30. It wasn’t until then that I came to have enough perspective to understand any number of things. And since then, of course, I’ve come to understand more and more and so what little I did understand at 30 barely seems to qualify for adulthood now. But that’s only natural. The more you know, the less what you knew before seems to mean.

Pubic hair.

An adult is actively responsible for themselves- food, shelter, clothing and being the legal adult age for their land. If you wait for social maturity to set in then continue to see 20+ year olds still mooching off their parents, still waiting to “find their passion”.

goddamn you @ratboy! that one was mine!

To me this always meant outgrowing negative juvenile behaviors, showing empathy towards others and taking responsibilty for yourself and your actions. Being an adult is a mindset more than being about age itself. There are many juveniles that are much closer to being an adult than many adults (by legal age) are.

For me, also, you’re an adult when you stop worrying about what you look like or what others think of you and worrying more about what and how you are doing as a person.