The poet is trying to explore when exactly he became an adult. Did he become an adult when he reached eleven or when his understanding about the world grew? Probably it is not the physical growth so much as the mental one which is the indicator of his adulthood. The journey from childhood to adulthood is that from innocence to maturity. In the last stanza the poet suffers from a sense of loss. With childhood he feels he has lost his innocence. Please share your feedback on [email protected]