Everyone has their own definition and it changes as they do throughout life. Besides, it's overrated. It's much more fun to be young at heart and enjoy life no matter what age you are.

Mature is...

Mature is another subjective ambiguous term. Using "mature" has both opened and closed doors in my use of the term. I like to think mature refers to someone who has some years behind them which has led to some level of wisdom and awareness about themselves, others, and what truly "floats their boat."

fully developed physically; full-grown.
"she was now a mature woman"
synonyms: adult, grown-up, grown, fully grown, full-grown, of age, fully developed, in one's prime, middle-aged
"a mature woman"

it means she's advertising as over 40, but may have hit the half-century mark.

Why not break it down into 10 replies 31-35, 36-40, ... for the slow-witted among us who couldn't figure out your first post? Do you think we're a bunch of BELOWAverageEverydayJoes?  

As all of the others have pointed out, your chronological classification is meaningless without consideration of more important personal factors

writes six separate posts explaining what should have been in one.  It might be the last stop before dementia.