Human Adulthood

I am curious about something germane to the discussions we've been having lately. It has to do with the quality of "adulthood" among human beings. It is, I think, a rare quality. I was wondering if the readers would offer their own thoughts on:

1) what is an adult human being?
2) What are the processes that create an adult?
3) what are the processes or events that inhibit the onset of adulthood?
4) At what point in your own life did you first consider yourself an adult?

This is important, and links together with many of our posts recently. Please add your thoughts.