Nobody in "Grownup" announces that childhood is over. The speaker simply files the paperwork. In eight short lines, the move from boyhood to adult life is told in the language of a closing account, and the coldness of that language is the poem's real subject.
The first stanza sets the loss against a single memory: "When I was a boy we used to play / at sea, that first music." The line break lets "play" stand alone for a moment before the sea arrives, as if play were the substance and the sea only its setting. Then comes a odd phrase, "that first music." The poem doesn't say whether the sea is the music, or the playing is. Either way, childhood is remembered as sound rather than as a picture. There are no ships or beaches, only a rhythm, which keeps the memory from turning into a postcard. The adult voice answers with "So has business taken me / from all my former delights." The "So" promises a cause but never explains it, and the inverted word order sounds formal, like someone reading out a statement. "Business" can also be heard as "busyness," and "taken me" makes it sound close to abduction: adult life here is not chosen but carried out. Even the vocabulary has shrunk. The boy had a concrete sea, while the man has "former delights," an abstract, plural, faded phrase.
The second stanza pushes the legal tone further. To be "quit of any obligation" is to be formally released, the way one is released from a debt. What the speaker is released from is "my missing key." A key opens locks, but it is also a musical term, and coming right after "first music" the double meaning is hard to ignore. I read the line as ironic. If the key is missing, nothing can be unlocked, so being excused from looking for it is less a freedom than an admission that the way back is closed.
The last two lines are the strangest: "My hand writes me from / the country of temper." The grammar turns the body into a stranger. The hand is the sender and "me" is the person receiving the letter, as though the speaker's own handwriting arrived from abroad. The line break after "from" holds back the return address for a beat, and when it comes it is a place with borders, a "country." That sets it against the sea, which has none. Childhood was fluid and unowned, while adulthood is territory. "Temper" suggests irritability, but judging by the surrounding music imagery it might also hint at tuning, or at the hardening of metal. The poem doesn't insist on any of these, and the ambiguity works in its favor.
The form is quiet but deliberate. There is no rhyme and no regular meter. Instead each stanza opens with its longest line (nine syllables, then ten) and follows with a clipped five-syllable line: "at sea, that first music," "to my missing key." Those short lines read like things muttered under the breath. The ear also catches a thread of long "ee" sounds running through "sea," "me," "key," and "me." Without any formal rhyme, the sound ties the speaker to both the sea he lost and the key he can't find.
What makes the poem worth reading is its restraint. It doesn't blame business, and it doesn't weep for childhood. Instead the register performs the loss: the boy's world is described in sound and water, and the grown man can only speak in terms like "obligation," "business," and "quit." The one-word title, "Grownup," sounds like a label or a job description. A good way to test the poem is to sort its words into two piles, the boy's and the adult's, and notice how few of the second kind are needed to make the first kind feel so far away.