Most females stop growing physically at age 15 and males stop growing at age 18. Our brains will continue to develop until age 25. So, by the time we reach 30 years old we have reached our peak in human physical and mental development. Yet, as Eugene Peterson points out, the most important growing up that we do is spiritual.
We never stop growing up spiritually and may never will. As Dallas Willard says, “We are unceasing spiritual beings with an internal destiny in God’s great universe.”
What are we trying to grow up to be? Paul says “we will grow to become in every respect the mature body of him who is the head, that is, Christ.” The last time I checked, I was no Christ so it may take an eternity for me to take on all that Christ can provide for me. But I can start now and I am expected to start now.

Evangelicals have traditionally put emphasis on being born again in a spiritual sense. But what birth doesn’t then include growth? Yet, so many Christians do nothing to foster their spiritual development. They are thinking that it is optional. Is it optional for an 11 year old to be potty trained? That would be ludicrous in most situations and it is ludicrous for a follower of Christ not to Grow Up.
In so many ways, we set up our children for success by placing them in situations and giving them opportunities that enhance their physical, mental, and emotional growth. We have to find ways to do the same for our spiritual growth. We often just see things like spiritual disciplines, Christian community, and right thinking as nice add ons for those that want to be serious about their faith but not for your average person.
Who wants to be average when we have the potential to take on the full stature of Christ? This is what Christ desires for you. Never stop Growing Up.