There are 4 kinds of maturity that I have found.
Physical Maturity:
Puberty...enough said. You can look up the growth hormones if you are more interested in this subject.
Emotional Maturity:
This is the realization that we have feelings, and these feelings are very powerful in our lives. They give our actions and our situations meaning. When a loved one die, we are exposed to grief and sadness. When someone attacks your or takes away your stuff, we get angry. When we see someone of the opposite sex who matches our own definition of beauty and grace, we swoon over with romantic feelings (probably lust or the "in love" stuff...which is basically more hormones). To become more mature in this aspect, we learn to control our feelings. We do not let ourselves become overcome with grief, which leads to depression. We do not let our romantic feelings consume us, leading us to hurt others. We do not let our anger boil over to rage and violence, which marks us as animals and oversteps many social and moral boundaries.
Having full control over our feelings allows us to fully enjoy them in the moments, and employ them in our lives for maximum effect without becoming slaves to them. It is also the ability to act fast and take control/command in dire situations.
Social/cultural Maturity:
The first example I think of is one
of a child soldier. A kid who is no longer a kid. The 8 year old who
was kidnapped, forced to kill his parents, forced to kill other parents,
forced to kidnap and enslave other children to become soldiers. These
children have been robbed of their childhood and its fun, and thrust
into the 'real world' a little too early.
In a more American culture, we think of it as getting an education, building a career, having a reputation in the community, owning a house and car, pursuing hobbies established by culture as "acceptable for adults." It means having a secure bank account and social standing. It also means having a wonderful family and taking good care of them. It looks down on childish things, like staying in your parent's basement playing WoW or LOL/Dota. Back in the day, it meant 12 year old boys became men, 12 year old girls could get married.
The first instance of this in our lives is that moment in our childhood that we realize that the world
doesn't revolve around us. We are not any more special than other
people. We cannot be the hero we perceive ourselves in our daydreams. Our dad cannot kick every other dad's butt. We need to have realistic dreams and goals. We also realize that people are not made equal. We will all have our strengths and weaknesses, and society determines which strengths are better, and which weaknesses are more pitiful. It is when we understand that the world is truly cruel and unyielding, and we are going to have to work for everything we have in our lives. There is no such thing as entitlement.
Another part comes with age aka experience. Knowing when to act and when not to act. Knowing what is truly important in life and what isn't. Knowing when to take responsibility and how to execute it.
Spiritual Maturity:
Luke 8:14 - People who worry or focus on life's pleasures and riches cannot mature.
1 Corinthians 2:6, Colossians 1:28 - People with wisdom grow more mature. (See James 3 on the difference of spiritual wisdom and earthly wisdom; Proverbs)
Ephesians 4:13, 2 Peter 3:18, 1 Peter 2:2, Matthew 4:4- Learning more and more about Christ (which should be primarily done through scripture...Bible literacy).
Ephesians 3:15 - Learning to speak in Love (and learning more about Christ's headship).
Philippians 3:15 - Following Paul's example and teachings, as well as our elders.
Colossians 4:12 - Knowing God's will and be firm in faith.
Hebrews 5:14 - Knowing the difference between good and evil.
James 1:4 - Persevering through trials and have patience.
Ephesians 4 - Being one with the church, making peace and unity. Finding our calling through the Holy Spirit. To have love and truth for our brothers and sisters.
Hebrews 6:1-2 - Having faith and avoiding sin. Full understanding of the Gospel.
Philippians 1:15 - Preaching out of love for our brothers and sisters and their growth, not out of envy or competition.
1 Timothy 3:6, 2 Corinthians 2:7 - Humility (I am sure there are many more verses for this).
Philippians 3:12-14 - Continuation of the desire to grow.
Romans 12:1-2 - Do not be conformed to the world. Our entire lives is an act of worship. God's will.
Note that I am hardly someone who has the right to talk about maturity, nor am I fully mature in any of these aspects (need to lose weight).
Edit:
https://www.youtube.com/watch?v=fLWRLjJe0hs (this guy is like the Bill Nye of Christianity)
Romans 12:1-2
Romans 12:1-2
