Life isn't static but dynamic, being susceptible to changes and so is the biological human.

No one remains a child, and so will you not remain as a teenager. Hence, the emphasis is laid down that one prepare towards adulthood in embracing full responsibility and independence.

As the saying goes; if you fail to plan, you have planned to fail. And the amount of time invested in planning will determine how much is executed. The teenage phase is a preparatory ground for adulthood. A stage of mental, intellectual, social and financial development in order to successfully strive as an adult.