When you call someone "mature," what do you mean?
Here’s my rough pass at defining it.
Emotional maturity indicates your ability to: manage your emotional state, adapt your behavior to your environment (know when to be silly and when to be serious), read and respond to social cues, not let one-off events hijack your system, and avoid hitting the extremes of the joy-misery continuum on a regular basis (ie, ecstasy and misery should be infrequent events).
Intellectual maturity is about knowing what you don’t know (ie, knowing the limits of your own knowledge), deploying what you know in way that’s coherent and consistent, entertaining ideas different from your own and accounting for such differences in your worldview, and in general bowing down to my friend Eliezer and his twelve virtues of rationality and avoiding the many corruptive heuristics he outlines on Overcoming Bias.
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?