Here's a smart bit on maturity via Ben Casnocha.
The most intriguing piece and then my thoughts:
Note that someone can be mature but also lighthearted, funny, laid-back, etc. In other words, mature is not synonymous with uptight.
While we've all met exceptions, in general emotional maturity and age are highly correlated. The younger you are, the less emotionally mature. Intellectual maturity seems less correlated with age. While it's hard for me to think of an adult who regresses on the emotional maturity scale, it's easy to think of adults who have become so set in their beliefs that they become less intellectually mature. They are less interested in tracking truth than confirming long-standing beliefs. Their total knowledge might be more than a young person, but how they deploy that knowledge is less sound.
This theory is not road-tested, so I'm interested in your comments and revisions. How do you think about "mature"? Do you think about it in these two categories? Do you, like me, have a gut feeling on someone's emotional maturity soon after meeting him or her?
I fully agree that mature does not necessarily mean uptight, though I'd add that it often does. I've fallen trap to this myself from time to time and it takes a lot of effort to "loosen up" sometimes.
And I'd never thought about mature in intellectual and emotional terms, because I feel you can't break it down into two pieces. Rather, I feel it's this all encompassing term that attempts to define a personality trait/characteristic that isn't actually definable. So I think it's a great attempt to try and define maturity, but you just can't do it. In fact, I see maturity as one of those "it" traits/characteristics; you know if someone has got it, but it's tough to define what "it" is... so to Ben's last question, yes, I have a gut feeling on someone's overall maturity.