Local parks are public spaces that can facilitate social interaction. However, the types of social and group activities older people engage in while visiting outdoor recreational spaces, and how these activities are affected by community interventions, have not been adequately evaluated. This study assessed older people’s social interactions and group participation at outdoor age-friendly exercise spaces (Seniors Exercise Parks) before, during, and after the implementation of a community-based intervention framework. A central component of the intervention framework was a volunteer-led program, which included community training, the delivery of group exercise sessions, and community activities and promotions to support engagement. Older adult visitor numbers, accompaniment, and social interactions were assessed using observational audits and intercept surveys conducted at six Seniors Exercise Parks, over 15-months. The data was reported descriptively, and generalised linear models were used to examine the impact of the intervention framework on the number of older adults participating in group and other social activities. The number of older people observed participating in group activities at the Seniors Exercise Parks increased significantly during (IRR 10.25; 95% CI 4.19, 25.08) and three months after (IRR 10.06; 95% CI 3.12, 32.43) implementation of the intervention framework. The proportion of survey respondents who reported participating in group exercise increased by 62% following implementation, while those who reported engaging in social interactions increased by 33%. Outdoor age-friendly exercise spaces – supported by community-based interventions that include volunteer-led programs – can facilitate sustained increases in older people’s social and physical activity participation, providing benefits for population health.