How does this story explore the theme of youth?

Oates's short story is compelling because she is able to expose the frailty of youth. In a culture obsessed with being young and associating youth with power, Oates offers a contrary perspective. The story demonstrates how the allure of youth is illusory and a potential dangerous mirage.
Arnold Friend is one of the best examples of the illusion that is youth. It becomes clear that he is much older than he appears to be. Youth is the mask that he uses in order to perpetrate his crimes. He first appears in a popular hangout for kids, blending in because of his youthful appearance. The supposed uniqueness of youth is actually a conformist mentality because of how fashion dominates individual choices. Arnold is perfectly fit for this because fitting in is his modus operandi in terms of moving closer to his intended targets. His car is one that appeals to young people, complete with the slogans that young people speak. Connie recognizes that his outward appearance of youth masks someone older, pasted together with makeup and lifts in his shoes. Connie would not have given Arnold a second thought had he originally appeared his age. It is because he is young that Connie pays attention to him, and thus seals her own fate.
Connie's youth is also an example of illusion. Connie believes that she has power and control. She is scornful towards the more mature visions of domesticity that her parents and sister represents. At the same time, she believes that because she covets social popularity and her own status is central to her being, she holds power. It is only when Arnold threatens her life and the lives of her family that she understands the frailty of her being young. In the final moments of the story, Connie actually acts older than anyone else in her condition of self-sacrifice. Connie rejects youth in favor of maturation, thereby causing her own destruction.
Interestingly enough, Oates's construction of Connie's parents is one where the immaturity that is often associated with youth is present. Connie's parents are "immature" in the sense that they are out of touch with their child, unable to form a bond or provide the nurturing environment that a teen like Connie needs. Their failure to provide structure is seen in the story. It is evident in their failure to demand clear answers to the most basic answers that govern all parenting of teenagers: "Where are you going?" and "Where have you been?" In being able to display parents who are immature in their failure to provide boundaries and expectations, Oates suggests that the folly of youth is not limited to children.
Youth is a "runaway train" that deludes people into believing they have control. The reality is far different. The derailed train is evident in the terror of Arnold Friend and the victimization that he causes.