So first we have to understand what I mean by “life.”
It must not be simply growing old, it must be growing up. And these are two different things. Growing old, any animal is capable of. Growing up is the prerogative of human beings.
Only a few claim the right.
Growing up means moving every moment deeper into the principle of life; it means going farther away from death—not toward death. The deeper you go into life, the more you understand the immortality within you. You are going away from death; a moment comes when you can see that death is nothing but changing clothes, or changing houses, changing forms—nothing dies, nothing can die. Death is the greatest illusion there is.
Osho. Maturity: The Responsibility of Being Oneself (Osho Insights for a New Way of Living) . St. Martin's Press. p.ix
Comment: Growing old and growing up are two different things. The choice is ours. Many people are in denial and unconscious of fact that they have a choice. Unitarian Universalism requires that people become consciously aware of their choice when it asks them to covenant together with others to affirm and promote the fourth principle to affirm and promote the free and responsible search for truth and meaning.
Unitarian Universalism asks people right up front to take responsibility for becoming oneself by formulating and understanding their own faith, their idea of what Paul Tillich called their "ultimate concern" rather than just going along with what other people expect and require.
Socrates taught that an unexamined life is not worth living. If most people are asked, "What makes you tick?" they become uncomfortable as if they have been put on the spot.
The covenant of Unitarian Universalism asks people to come to awareness of their own state of being. This can be a frightening think initially, but as one searches one finds more peace.
People come to a point in their lives gradually or suddenly that what they have been taught by society is illusional and that there has to be a better way to live their lives.
If we put maturity on a scale of 0 - 10 with 0 being newborn and very immature and 10 being fully self realized, actualized, self-aware, enlightened human beings are mature are you? How mature are the various people that you know well in your life?
My experience of Unitarian Univeralists is that many of them who actually understand and apply the principles in their lives are very mature. How ever I have also met many UUs who are just along for the ride and don't take the faith seriously in terms of working the principles in any kind of meaningful way.