What metaphors are used in Birches by Robert Frost?

The poem, Birches, uses the metaphor of a boy swinging on birches as a metaphor for youth and then corresponding old age. It is a comparison of the joyful abandon of youth with the struggles and burdens that adulthood brings with it. It is clear, then, that Frost prefers youth to old age when he writes, "One could do worse than be a swinger of birches."