you are referring to the public commonly accepted conception of maturity, I'm asking about your own personal criteria
If you ask me, this is just a word, which people use, like love. It's too vague. It has some meaning, but it's so vague, that it can't be put in a word. I'm fundamentally not sure if people really grow. Sure, people learn things, all the time, maybe this is what should be called the process of maturity. However, I'm not sure to what extent this learning is real, and do we really grow. If it was up to me, I wouldn't divide people into mature and immature, because strictly, there's no way to make such separation.
About the common notion, just realized one more thing. It seems maturity is related with the desire/ability to: control, influence, own, dominate, direct, be "independent" (which I think is physically impossible, and is thus a verbal fraud), even manipulate... okay, I'll stop here. Such qualities I find as unnecessary, and interfering with the learning openness in oneself and towards others, so such notions of maturity can be also seen as immature.
Besides, I actually find impossible for anyone, including myself, to give definition outside of some culture. If people in my country are very mature on average, this changes my perspective to what is what; similarly, in the opposite case. Everybody who writes on maturity is biased by that. Eg: I probably wasn't going to be so tolerant of immaturity if I was surrounded by crowds of very immature and aggressive people. Which is the case - when I was a kid! I've been one of the most mature kids, just to contrast what has been around me. Now I think I'm approaching the other direction.
P.S. The language even tricks us, me and you, when you ask me about my "own personal criteria", because maybe such thing doesn't exist. I wouldn't have imagined the notion of maturity on my own, and the same applies to everybody else.