Final answer:
The central theme of the text is that growing up and aging happens quicker than expected, and youth should be appreciated.
Step-by-step explanation:
The central theme of the text is that growing up and aging happens quicker than expected, and youth should be appreciated. The text mentions that adolescents struggle with developing a sense of self and often try on different identities to see what fits. It also discusses the challenge of embracing integrity in old age, which can lead to creativity and preparing for the end of life.