W. D Wetherell's story “The Bass, the River, and Sheila Mant” is about two teenagers who meet during one summer vacation. This kind of story is often called a “coming of age” story, (in literary circles sometimes referred to as a “bildungsroman”). The focus in such a story is usually the development of the main character, including some sort of significant character change.
Teenage years are all about change, whether we like it or not. While the most obvious changes are occurrings to our bodies, we are also changing psychologically, socially, morally, and spiritually. Wetherell chose these young characters so that he could focus on the important lesson that the unnamed male learns on his ill-fated date with Sheila Mant.
The reader finds out pretty quickly how old the narrator is; here are the first couple of lines from the story:
There was a summer in my life when the only creature that seemed lovelier to me than a largemouth bass was Sheila Mant. I was fourteen.
That's a nice opening sentence, packed with meaning. We know immediately that the narrator is going to be torn between two things: his love of fishing and a girl.
It doesn't take long to find out how old Sheila is. In the next paragraph the narrator tells us:
Sheila was the middle daughter—at seventeen, all but out of reach.
She is “out of reach” in more ways than one, but the age difference is certainly important at that stage in life. By the end of the story Sheila has dumped the narrator at the fair for an older guy, Eric Caswell, who offers her a ride home in his Corvette. The narrator then tells us, in the story's final paragraph, that he learned not to make that sort of mistake again.