Objective: Posttraumatic stress disorder (PTSD) has been frequently reported during the COVID-19 pandemic. Although there is evidence for age differences in PTSD symptoms, many studies assume that PTSD is a latent entity and overlook such differences. To address this gap, the aim of this study was to use network analysis to examine and compare PTSD symptom networks across different ages. Method: During the COVID-19 pandemic, 1,153 young adults and 683 adolescents were selected to complete self-report questionnaires. Results: Two networks shared core symptoms (e.g., exaggerated startle response and irritability) in the arousal cluster. A network comparison test indicated that the young adult network was significantly stronger than the adolescent network. Except for exaggerated startle response and lack of positive emotion, symptoms in the young adult network exhibited higher centrality than in the adolescent network. Conclusions: An age difference in PTSD at the symptom level and provide practical evidence that could inform mental health interventions after the COVID-19 pandemic. Clinical Impact StatementThis study demonstrated that exaggerated startle response and irritability are core symptoms of both young adult and adolescent PTSD networks. Psychological interventions for these populations during the COVID-19 pandemic should focus on these two symptoms. There were significant age differences in the PTSD networks: The PTSD network of young adults exhibited higher centrality. This suggests that young adults have more severe PTSD and that treatment for this population should be a priority during the COVID-19 pandemic.