Being an adult has nothing todo with chronological age
. I know some 16, 17 year olds who are years ahead, emotionally
, rationally, of some 21+, even 25 year old people i am acquainted with. It's how you've lived the time you have, what you've done to it and what it's done to you, that shape these things.
a 27-year old, pampered and spoiled all his life, still being paid for by his parents, has not *lived*, really, in many senses. A sixteen-year-old, working, paying his own bills, maybe living in his own place, is far more adult in he has taken on more responsibility.
The people who can drag their heads out of the clouds and deal with practical things, examine the world logically and understand--grok--how it works, these are adult.
People who have known extreme pain and hardship, and have survived it and become stronger, better, learned more about themselves in any tiny way... they are 'growing up' from this. becoming more adult. A person for whom everything goes perfectly may be adult, but they lack the experience, the knowledge that comes from hurt.
A person who is mentally an adult, or at least as much of one as the can possibly be at their stage of development--these are the people who appear "ageless"--you look at and you can't tell if they're 17 or 27. The people who are chronologically 'adult' but act not like it, the 21-year old person who you *know* is a college student because they *act* like one... may be older... but not adult.
It's not an age thing... chronology is meaningless. it's a frame of mind.