"When the melon is ripe, the flowers will be beautiful" comes from the poem "Zhong Chao Wrong" written by Cheng Gai in Song Dynasty. The full text is as follows:

After the flowers fall in bloom, the water flows eastward. There is no plan to stay in spring. Who planted incense in Du Ruo and dreamed of returning to Yangzhou. In the year of broken melon, the flowers are gorgeous and the willows are tender. Don't say that Liu Lang has frosted his temples. His talent has not been released in the spring.

"It's the year of broken melons, and bloom is gorgeous, with a bright future." It means that Yangzhou's singer is sixteen years old, with a pretty face like a shy flower and a slender waist like a willow branch. "Broken melon" means sixteen years old.