There is no definitive pronoun used to describe the person addressed by the poem's speaker, and, therefore, we must conclude that this sonnet could address either a woman or a man. Because of its context within Shakespeare's oeuvre, people tend to assume that the speaker addresses an attractive young man; however, I always caution my students against making assumptions about a poem based on things happening outside of the poem. Since this speaker never specifies, I believe the sex of the person being addressed is left open for our interpretation. Certainly, it seems possible that the speaker could describe either a man or a woman as "lovely" and "temperate"; likewise, the speaker describes the addressee's "eternal summer" and the "fair[ness]" that the speaker hopes to prevent from perishing from the earth forever by writing these words. Both men and women can be attractive and worth preserving, in some way, from inevitable death.