The claim of this article is that first-time voters in Pennsylvania will have a big influence on which way the state votes in the upcoming presidential election. At first, it was difficult to discern the credibility of this article because the majority of its claims are backed up by interviews done by the source, ABC News, and not by outside sources. However the article did mention some statistics in the first several paragraphs that I was able to trace to other sources. For example, the author stated that "fewer than half of 18- and 19-year-old voters nationwide cast ballots in the 2020 election" and provided a direct link within the article to the source of that statistic, an article from the Center for Information and Research on Civic Learning and Engagement at Tufts University (linked here). This article corroborated ABC News' claim, stating "We also estimate that voter turnout among young people ages 18-19 was 46%." However, the Tufts University source doesn't appear completely reliable because it has no author and its only source of information is the university's own estimates from their Census 2019 American Community Survey, which is a table of data with little information aside from states and numbers. There's no information on how the data was acquired or who collected it.
The ABC News article also says "Pennsylvania teens have historically participated at a higher rate than the national average and may be helping to close the gap with other voting groups, experts say." This is problematic because this is a bold claim and it is unclear who the actual experts are that the author is referring to. When I copied this into my search bar, I found no other articles covering the topic of Pennsylvania teens voting above the national average. Furthermore, when I searched up the title of the article ("Could Teenage Voters Swing Pennsylvania?") I found no websites covering the same topic with the same statistics aside from ABC News.
ABC News also claimed that "more than 70,000 young Pennsylvanians reach voting age every year" which I was able to trace to an article by the Civics Center, which has no evidence or outside source to support the claim.
Overall, I think that this article has some important insights as it features quotes from new voters in Pennsylvania and discusses actions that they are taking before the election. However, there is little reliable data on it's claims that teenager voters will determine Pennsylvania's voting outcome, and I wasn't able to find their statistics from any other source, so I think that while there may be some truth to the claim, it is most likely exaggerated. All in all, this appears to be more of a story piece about voters at Martin Luther King Jr. High School than a factual article about the impact of new voters in Pennsylvania.