In what sense is there a generation gap, and why is the failure of one generation to understand another's culture, customs, and heroes central to the story "Where Are You Going, Where Have You Been?"

Joyce Carol Oates was very concerned with the youth culture of the 1960s and the "Free Love Movement" in which indiscriminate sexual activity among youth became popular. Then, inspired by Bob Dylan's song "It's All Over Now, Baby Blue," Joyce composed her haunting story with a character who is imitative of the 1950s serial murderer Charles Schmid. He was a handsome but short man who stuffed his cowboy boots with newspaper so that he would appear taller, just as Arnold Friend appears to have done as he "stand[s] in a strange way." Schmid had many girlfriends that he seduced. He killed some of these girls after tricking them into going to the desert with him, where he later buried them.
Some of the lyrics of this song express the idea of the impermanence of anything in life:

You must leave nowTake what you need, you think will lastBut whatever you wish to keep, you better grab it fast--

Joyce ties the generation gap to this concept. Indeed, there is a disconnect between Connie and her friends and their parents, who do not seem to understand the changing culture of the time. When the father of Connie's best friend drives the girls to the shopping center where they wander through stores and sometimes walk to the movies, he "never bothered to ask what they had done." Connie's parents do not realize that she wears her blouse one way at home but "another way when she was away from home." Nor do the parents inquire about the other teens with whom she and her friend associate. For instance, after Connie has supposedly been at the movies (but instead spent three hours with a boy at a restaurant), her mother merely asks "...how the movie was, and Connie said 'So-so.'" The mother does not ask questions that are specific enough to indicate whether or not Connie actually watched a particular movie. Further in the narrative, the parents do not insist that Connie accompany them to a barbecue at her aunt's house, allowing Connie to say nothing more than she is not interested. If Connie's parents were aware of the changing culture of the time, and if they supervised Connie's actions, questioned her about her activities, and insisted that she partake in family gatherings, Connie would not have been alone and vulnerable to her "trashy daydreams," the seduction of music, and the predator Arnold Friend.
https://genius.com/Bob-dylan-its-all-over-now-baby-blue-lyrics