Background: Research examining the psychological impacts of social media often yields inconsistent findings, largely due to a reliance on aggregate usage metrics that obscure specific user behaviours. Furthermore, evidence suggests age-differential psychosocial outcomes, wherein younger populations frequently experience digital distress, while older adults demonstrate psychological resilience. Methods: To address these methodological limitations, this two-wave longitudinal study (baseline N = ~400) compares younger and older adults by operationalising social media use into distinct motivational clusters: status-oriented, relational, and escapist. Participants completed measures for depression, anxiety, loneliness, mattering, and self-control. Results: Preliminary cross-sectional analyses reveal that younger adults engage predominantly in status-oriented and escapist usage, which significantly correlates with heightened psychological distress. Conversely, older adults prioritise relational use, which acts as a protective mechanism significantly associated with enhanced perceived social support, a greater sense of mattering, and reduced loneliness. Forthcoming longitudinal analyses will evaluate the temporal stability and predictive validity of these usage pathways over time. Conclusions: The relationship between social media use and psychological well-being is more closely associated with specific use motivations than with overall duration. These findings provide insights for researchers and policymakers, suggesting that interventions aimed at supporting healthy ageing should focus on cultivating purposeful, relational digital engagement rather than simply limiting screen time.