The poem is in Petrarchan sonnet form—sort of. Because it is not a traditional sonnet—no meter and no rhyme scheme—we could maybe say it is “inspired by” the Petrarchan sonnet form.
What I love about the Petrarchan sonnet form is that it consists of an octave (eight lines) followed by a sestet (six lines) that are in tension with each other—the tension point is actually built into the poem. Poems love opposition because life has opposition, and a poem more than anything wants to talk about what it means to be alive.
Traditionally, the first line of the sestet invites a turn (a volta) in which the poem changes direction. Often this is achieved with the word but or yet. In this poem, we could think of the turn in a few ways:
1) In the first stanza life has the pen, in the second, “you” do.
2) The first stanza is about the present moment looking to the past, and the second is about the present looking to the future.
3) The first stanza is about the known, and the second stanza is about the unknown.