I was picking flowers, playing by my door, When you, my lover, on a bamboo horse, Came trotting in circles and throwing green plums (2-4)
We can see some pretty conventional gender role play in this scene from the speaker's childhood. The girl (the speaker) is picking flowers, and the boy (the lover) is trotting along on a toy horse. This is kind of the equivalent of girls nowadays playing with Barbies and boys playing with cars and guns. In other words, even as children, we can see that gender roles are differentiated through play.
And I lowered my head toward a dark corner And would not turn to your thousand calls (9-10)
Again, here, we see the speaker depicting her relationship to her hubby in terms of conventional gender roles. It's her hubby who calls a "thousand" times to his shy wife. In other words, he is the "active" man who initiates things, while she cowers shyly in a corner.
But at fifteen I straightened my brows and laughed (11)
This is the first time in the poem where we get a sense of the female speaker growing in confidence. Now she's laughing openly with her sweetheart; she isn't frowning anymore. She seems to be becoming an equal to her husband, because she clearly feels comfortable expressing herself.
…Then when I was sixteen, you left on a long journey Through the Gorges of Ch'u-t'ang, of rock and whirling water (15-16)
In these lines we again get a sense of gender relationships that are divided according to conventional norms. The husband is the one who goes off exploring on his long journey, while the wife, the speaker, stays home waiting for him. This feeds into the idea that men are the adventurers and explorers, while the woman's job is to stay put and look after the home.
And, because of this, my heart is breaking And I fear for my bright cheeks, lest they fade. (25-26)
Stereotypically, this speaker is a woman who worries about her looks, about her "bright cheeks" fading. Her preoccupation with looks here again emphasizes (again, according to the stereotype) that we're dealing with a female speaker here. It's women who have to worry about being pretty, not men—which is totally unfair, we think. Of course, the speaker's cheeks are fading because she's heartbroken and she misses her hubby so much. But the fact that she is worrying about how her cheeks look suggests that the speaker of this poem is a pretty "conventional" woman, according to thousands of years of patriarchal norms.