Housman’s “When I Was One-and-Twenty” takes the form of a cautionary fable, the unnamed speaker relating what happened when the speaker failed to take the advice of a “wise man.” The opening two lines establish the speaker’s age at the time—21—and contrast the speaker with the figure of the wise man. By implication, this latter man is older and thereby more experienced in the ways of the world—and, in particular, love.
The whole poem has a very child-like sound to it, evoking the tone and rhythm of a nursery rhyme. Here, in particular, the /w/ sounds in "when," "was," "one" and "wise" are particularly light and playful. This alliteration perhaps suggests the youthful naivety of the speaker at the time in question.
Lines 3 and 4 cite the wise man’s advice. Essentially, this advice compares falling in love to a kind of financial transaction, saying it would be more sensible for someone to give away all their money rather than risk giving away their heart (“crowns and pounds and guineas” are all types of British coins). The polysyndeton in line 3, with the repeated “and,” emphasizes the wise man’s words, but also contributes to the poem’s overall playful sound.
As with much of Housman’s poetry, critics are divided over whether his poems actually are naive and adolescent, or whether they deliberately mimic the kind of thought processes and feelings that come with being adolescent (Housman himself wrote this poem in his mid-30s). The reader might also question the usefulness of the wise man’s advice. That is, to what extent can falling in love—and being heartbroken—really be compared to giving money away.
The wise man’s words are especially musical:
“Give crowns and pounds and guineas
But not your heart away;
The assonance of /i/, /ow/, /a/, and /aw/ sounds highlighted above gives the man’s words the air of an old saying, advice handed down from generation to generation. The internal rhyme of "crowns and pounds" adds to this effect. But it also makes his words sound kind of throwaway—easy to remember, but hard to put into practice.