This poem turns on its head the idea that a tenth birthday is a joyous occasion. Instead, the young speaker laments the loss he is feeling as he grows older. The poem shows the pain of maturing from innocence to experience.
Turning ten makes the speaker feel sick: he imagines his maturation as a typical childhood illness of his period, such as the measles, the mumps, or the chicken pox, using these diseases as metaphors for getting older.
The speaker primarily regrets his loss of imagination. He writes of the end of magical thinking:
At four I was an Arabian wizard.
I could make myself invisible
by drinking a glass of milk a certain way.
At seven I was a soldier, at nine a prince.
Now, however, at ten, he lives in a more prosaic reality: "the late afternoon light" falls solemnly against his bicycle, "all the dark blue speed drained out of it."
The speaker employs apostrophe, addressing an absent "you," an adult telling the child he is too young to be looking back nostalgically at his past. The boy, however, attributes this to the adult having forgotten what it is like to be a young child.
Growing up brings with it an awareness of the reality of pain. The speaker knows now he is not filled with "light" but that if he falls, he will "bleed."
The speaker's childlike voice opposes and yet highlights the poem's melancholy theme. The poem is in the tradition of Romantic verses that acknowledge the special spirit and innocence of the young child, such as Wordsworth's "My Heart Leaps Up," which states "the child is the father of the man."