Adults?

In the dictionary, the definition of an adult is a person who is fully grown, but if I think closely about this I don’t know any adults because if you take someone to be grown to the level of meaning mentally then there isn’t one adult on this planet.

This I think might explain why when we look around is we see such childish behaviour, countries acting like children pointing at one another and say “be he started it”
But this is just one example, another example is the emotional blackmail that is placed on people by family such as but if you move away we won’t see you, It’s been my observation that people don’t seem to ever seem to see what is best for others might mean doing something you don’t want.

So I ask a simple question is it too much for us to grow up mentally as well as physically?

I don't believe I'm asking for the impossible just the reasonable.