What makes an Adult?

Over on PS-238 I found this comment.

"Totally agree. But for a slightly different reason. A ‘true’ hero mindset is: “Who am I responsible for?” The question that she is being asked is, “Are you ready to be responsible for everyone on Earth?” Glory and prestige are not even a part of the issue. 

And the “Who am I responsible for?” question is a question every mature adult asks themselves. Children are responsible for no one. Mature adults are responsible for themselves, their better-halves, their children, and the other people and children around them. 

So the real question to Julie/84 is, “Are you ready for this level of responsibility?”

On a personal note, I have met some very mature 12 year olds that I would trust with my life and I have met some very immature 30-somethings."

I'm sorry that doesn't link to the actual comment, the comment section there isn't set up for that so I linked it to the actual strip in question.

Now, think about what that comment is saying.  It is asking who is responsible, and for what/whom are they responsible for.  And the last sentence is very striking.  Yes, I have met children, who have more maturity and sense of honor and responsibility than some graduate students.

So "What" makes and "Adult"?

Comments?