This is a question I’ve come back to many times in my life, and it’s a tough one. As a kid, there seems such a difference between kids and adults that it appears dichotomous; first you are a kid, then you are an adult. The actual transition is so gradual, though, it’s confusing.
The rituals our culture provides are pathetic and seem more and more pathetic in retrospect as I get older: graduating from high school, registering for the draft, being able to purchase pornography, being able to drink. Even graduating from college is pathetic in terms of an adulthood ritual. I just watched a bunch of people graduate from UO and they sure seemed like kids to me–certainly not children, but still dependent on parents, still at best vaguely aware of what they would do with their life, still without anyone depending on them.
There are biological markers, but no one I know was an adult at sexual maturity, even if they did manage to have sex or even conceive. Physical maturity doesn’t seem to correlate with emotional maturity at all. And brain scientists keep pushing back the age at which our brains are fully mature–lately I’ve been hearing 25 or 26, but fifty years ago it was 7, so in another fifty will we not have mature brains until we’re 45?
We could use financial independence, but what does that really mean? That we only ask our parents for help when we get into really expensive trouble? We could wait to say we’re adults when we are supporting our parents, but that’s tough for us Gen-Xers, whose parents will mostly die richer than us for social and political reasons.
I imagine the “real” answer is a combination of a bunch of factors, not amenable to a simple scheme, but I have come up with two, simple, adult-identifying schemes to offer. They are pretty subjective and fail to provide a distinct moment in which adulthood occurs, but they are my favorite ideas about this so far.
1) Gratitude for parents: We gradually become capable of understanding what our parents have done for us. Perhaps we are adults when we are able to, without idealizing them, fully appreciate our parents. This could be a good indication that we have moved past egocentricity.
2) The ability to distinguish threat from non-threat: A bus bearing down on us is a threat. Someone disagreeing with our opinion is not a threat, even if the disagreement is strongly worded and about religion, politics, or contentious-topic-of-your-choice. Perhaps we are adults when we can easily respond in an appropriate manner to the reality we are presented with–when we can consistently use reality testing.
Nathen's Miraculous Escape 
June 27, 2010 at 8:08 am
So, then, does that mean that by your definition, a great many people never reach adulthood? There are obviously people who never come to respect their parents for one reason or another. But I think even more common than that are people who never grasp the ability to argue dispassionately about topics such as religion or politics.
June 27, 2010 at 10:16 am
I’m thinking of my criteria as ways of identifying adults, not necessarily identifying non-adults. And mostly I’m thinking about them as ways of checking my own progress in maturity. You might say these criteria are Nathen-centric–possibly not applicable to other people. And yes, if used universally, this way of defining adulthood creates a need for a new term for non-adult people who have grown up.
June 29, 2010 at 9:37 pm
Personally, I have no problem with a definition of “adult” that is not 100% serious and categorizes many people as never reaching adulthood.
After all, society has fairly recently invented the demographic “teenager”. We tell people they are no longer kids, but not yet adults, and provide insufficient ways to earn from adults much sense of belonging or self-efficacy. Should we be surprised they create their own, often self-destructive rules for belonging and self-worth? The whole concept of “teenager” is a crime of marketing.
In a parallel manner, politicians have fairly recently removed many of the rights and and responsibilities of adulthood. This is not always a bad thing–softening life’s harsh times can be a valid role of government. But it’s no surprise we are left with difficulty defining adulthood, and possible definitions that many people will never grow into.