Growing Up?

I was taking a very long bus ride today when I suddenly thought of BD's entry almost a week ago.

He mentioned about growing up.

Not growing up per se, but from that of an adolescent to an adult, mentally and emotionally.

This year is the 'coming-of-age' year for many of my peers as well as myself. We will turn 21.

I thought long and hard. What really makes us an adult?

Is it just the age of 21? Or the privileges we will have? Or the rights? Or the responsibilties? Or just the things we do can affirm our place in the adult world?

I think I know just the answer. But I hope I can get some opinions. Do you know the answer?