We all have been there.
Do you remember when your parents told you "you are still very young to understand", or "you need to have more experience to understand", and etc...
My question is when do we know a human being is mature to face whatever reality has to face?
In my opinion, maturity exists in a continuum, and as such, we are never prepared enough to face everything. An example I'd give is the increasing amount of mental disorder that our modern society is facing, from simple stress to PTSD (for instance the 9/11 accident). Now going back to children, instead of restraining them, I believe that we should instead help them to learn. Two major researchers have formulated distinct theories regarding children development.
A first one is Jean Piaget who wiewed children development as a serie of discontinuous stages marked by specific conflicts. This one is still very popular nowadays and still serves as a reference to judge children's development and abilities to udnerstand what's going on around them.
A second one is Lev Vygotsky, who viewed children development as a continuous process where social interaction was the key. Indeed for Vygotsky, children are beings that have disorganized thoughts and conceptions and need the guidance of a more experienced person in order to organize these thoughts and concept.
My opinion on this matter is that we are never mature enough to face everything that life has in reserve for us, and judging someone's maturity is difficult without knowing his complete background.
Sometimes we might feel very mature but a simple event that we've never experienced will make us go back to a previous stage so the only thing I can say if you really want to gauge one's maturity would be to trust your own experience and observe the other's reactions.
Does age have anything to do with maturity?
A more realistic example, Obama 40 something, Hillary 60 something does the older Human have more advantage for whatever reason to get elected?
I don't believe that age has something to do with maturity. As a matter of fact, within the last 10 centuries, humans' life expectancy has risen by about 30 years. Would it make us more mature than our ancestors? I doubt so or we wouldn't use ancient works and proverbs nowadays.
As I was saying in the previous part, maturity is in my opinion a result of your life experience and for example, someone who's never had any negative experience can be completely immature at 20 and act like a spoiled brat (forgive me the expression).
Here another one, now a days which age should we fix to decide when some one is an adult?
Is there a real response to that question? I doubt so. In most states in the US as well as Japan (somebody correct me if I'm wrong), the legal to be considered an adult is 21 while in countries such as France or Germany, it's 18. In some old cultures, one needed to perform an act to be considered an adult (I am referring to some African and native American rituals) and as long as one could accomplish it, it didn't matter how old he was (though most of the time there was an age limit). In the end, don't you think that becoming an adult or not has more to do with culture and society acceptance than anything else?