I spent all my life with teenagers and in a way I've become one. The most important thing to remember is they are adolescents - people in the process of becoming adults. Hell, I'm still doing that - one day I will be mature - one moment after I'm dead. Until then, I'm in process, like everyone else on earth :)
I agree with you if we are using the word "mature" in a strong moral sense, not necessarily constrained by the opinions of others.
At my death or resurrection, whichever comes first, I fully expect God to finish the task of "maturing" me in an absolute moral sense. In other words, from then on, all of my actions and interactions with others will be "morally mature," and will only and always proceed from love and result in greater good.
However, I also expect not to become static. I expect to continue to learn forever, to be filled with wonder and gratitude each new day, to be childlike in my engagement with Jesus and other people and the universe.
Meanwhile, I muddle on, "in process" as you say! ;)