Being self-corrective. I have been able to change my viewpoint many times in my life about various things, and admit it. Throwing away black and white thinking is also a sign of maturity especially when it comes to sex, relationships, the thoughts we have...

The ability to laugh at yourself, to think before you act, to take the time to research before speaking out on an issue, and to love your life and yourself.

Peeing a little if you laugh, having a "all nighter" which means you never had to get up to pee, Looking at a police officer and thinking they look to young .... Bending down thinking I can lift that up then twang! oh me sodding back! Going to get my haircut and the barber charges more to find it than cut it..... Farting more! Looking in the paper to see who has died .....

Maturity is inversely proportional to drama

with any luck one has enough info to sort out the rats from the chipmunks. One can evaluate a person with a fair degree of accuracy quite quickly. One can shy from risks and feel from the other person's point of view. One can also become more intolerant generally. One cares less about one's image but more about reputation.

Accept your own illogical mistake or immaturity and then try to grow up .

Immerturity is believe you are always right

Characteristics of a mature person:

One who is willing to accept responsibility for an error and make an honest attempt to fix it if at all possible.

One who is slow to anger and quick to move toward peace.

One who gives respect freely to all who earn it. Respect is not a right or something to be given on demand, but when there is reason for it, it is to be rendered up quickly.

One who listens to others and pays attention to what they say without interrupting.

One who tries within their capacity to understand to consider as many sides to an issue as possible before arriving at any conclusions. We are human, after all, and try as we might we all find it hard to be completely unbiased, but we should learn to do this to the best of our ability and constantly strive to get better at it.

One who when in the wrong can offer a sincere apology to the other.

The list is far too long for this venue, but these are some important ones.

Able to experience empathy. In my life experiences, the most mature and intelligent people are those best capable of expressing empathy for others.

Understanding that they can be wrong

I am not much on being a "grown up" or acting my age. Some people act like there is this rule book. I have never seen it and if I did, might read it but follow it just as I follow biblical books. But I think I am a very mature person when I need to be. I don't equate maturity with being grown up. I am mostly capable of adulting but enjoy my inner child tremendously and let out to play whenever I am not required to do the adult stuff.

Accepting the cold harsh truths of reality. That sone sicknesses have no cure. That some people are so much engrained into their way of thinking that pain is associated with thinking otherwise. Basically, acceptance of the worsts aspects of life. Not ignoring the reality of our society, no matter how close it might hit home.

Having the mindfulness of not being a d-bag when being a d-bag would be completely appropriate.

How would I know I have no intentions of ever growing up, seems like it would be a real drag. I don't take myself seriously enough to consider growing up.

I have a friend that tells me he did that and didn't like it so, he decided to revert.

Being able to change your opinion.
Being willing to really listen and pay attention to opposing views.
The ability to laugh at yourself.
The ability to own up to your own failures.
Someone who has high levels of integrity
The capability of being kind to those who have not been kind to you.
The ability to put off reward for a better outcome later

These and more. A person who has most of these qualities would be someone with a higher than average level of maturity and the age of someone isn't a quality indicator of maturity.

Depends on the person and the culture but I hear that archetypes and ideals of the perfect 'gender/role' might be something that exists across animals species (at least among social animals).

Ability to manage and recognize their own emotions, reckless actions are at a minimum, and how they manage responsibilities. Those are the three things that come to my mind when I think of a mature person. If you would like details let me know.

Taking responsibility for their actions.