Background/Objectives: This study investigated adherence to physical activity (PA) guidelines and associated sociodemographic factors among older Koreans from 2011 to 2020. Methods: Utilizing four public data sets from the National Survey of Older Koreans, the study included the data on 40,993 older adults 65 years and older in South Korea, collected between 2011 and 2020. Adherence to PA guidelines and sociodemographic factors were assessed through self-reported questionnaires. The data were analyzed using a two-way analysis of variance and post hoc tests. Results: Overall adherence increased from 39.1% in 2011 to 48.2% in 2017, then decreased to 37.6% in 2020 (p < .001). Men had higher adherence than women (p < .001). Age-related adherence peaked in the young-older group (65–74 years old) and was lowest in the oldest-old group (85+ years old) (p < .001). Marital status, education, and income were also significantly related to PA adherence (p < .001) across the years. Conclusion: Although continuous increase in adherence to PA among Koreans 65 years and older was observed, the decline in PA levels during the COVID era underscored the need for targeted interventions and well-informed health care policies to address demographic challenges. Still, considering that data were collected during the recommended social distancing period, a cautions interpretation of these findings is warranted. Significance/Implications: Health policies aiming to improve adherence to PA guidelines should prioritize Korean older adults who are female, belong to the oldest-old group, are single, and have low education and income levels, with the goal of enhancing health equity.