What is maturity? Perhaps it is an ongoing experience for all of us. We never stop maturing. The day we stop maturing is perhaps the day we stagnate.
We look at a young girl or boy and find that he/she isn't mature. What perhaps we mean is that she hasn't realized what the right priorities in life are, or doesn't understand the meaning of consequences.
Perhaps we meet a young man, but he cannot overcome a lost love. What we mean is perhaps that he needs to accept the truth.
Maturity is an ongoing process, it is one where we keep on learning new things, accepting new truths, so that we become in a way, different, new even. The Bible urges us to keep on re-new-ing our minds. To keep on maturing. To become "better".
It is in accepting beliefs, or rather truths about the world, about life, about people, about the mystery of God.
But when new comes, some of the old things must also go. Mistaken beliefs, assumptions, generalizations, simplistic ideas, fear, greed, cowardice, self-centeredness, anger, lust.
Maturity can also mean holding on to the truth in spite of societal pressure. So whether it's gaining new truths or holding on to it, it is in truth that we must grasp and hold on to.