This poem is a famous example of a type of literature referred to as "carpe diem" literature. This is a Latin phrase meaning "seize the day." Thus, in this poem, the speaker addresses all "virgins" or young women and urges them to marry now rather than wait until it is too late and they have lost their "prime." Note how the first stanza builds up this impression through the use of imagery:
Gather ye rosebuds while ye may,
Old Time is still a-flying;
And this same flower that smiles today,
Tomorrow will be dying.
In an implied metaphor, the "virgins" or young women are compared to the "flower that smiles today" but might have withered by tomorrow. Thus when we think about the tone of this poem we can characterise it as one of persuasive urgency - the speaker is really trying to encourage his audience not to "tarry" because if they do it might be too late.