Growth comes from different approaches. Maturity comes from learning by choice and/or circumstance. And it is only when we learn that we mature. It behooves us therefore, to learn every lesson that we are being brought through; most of which we can miss when we are not paying attention or simply dismiss as unimportant!
What we fail to grow in and develop at one stage of our learning curve, we can be in the danger of repeating it at a higher level, and consequentially at a greater cost. This is true of school, business, character, spirituality and just about every aspect of life as a whole. In that sense, our length of involvement or service, does not make us more mature individuals, it is the deftness through which we assimilate life lessons in the process that mature us. If that sense, it is possible for a 15 year-old to have the maturity of a 50 year-old, and the reverse also being true!
God has given us His Spirit because His expectation is for us to grow in Him (in the Spirit). His Holy Spirit teaches us all things, and in order for us to be like Him, we must yield ourselves to the process of maturation. Maturation is a choice. It is a lifestyle.