Demographic decline and population ageing present unprecedented challenges to housing systems in post-socialist Europe. With one of the European Union (EU)’s fastest shrinking populations, an underdeveloped social housing sector, and an ageing housing stock dominated by Soviet-era multi-family blocks, Latvia exemplifies these difficulties. Adaptive property reuse—repurposing underutilised buildings into age-friendly social housing—offers a potential solution, but its feasibility depends on complex economic, regulatory, social, and environmental determinants. This study investigated these determinants using a mixed-methods approach. Data were drawn from 312 survey responses, 15 policymaker interviews, 10 developer interviews, and focus group of 25 senior residents across Latvia. Exploratory Factor Analysis (EFA) was used to extract six determinant clusters: site selection, feasibility analysis, design and planning, implementation strategies, monitoring and evaluation, and scaling strategies. The findings demonstrate: (1) economic feasibility and regulatory clarity dominate stakeholder concerns, with financing gaps receiving the lowest ratings (M = 2.91); (2) implementation strategies emerged as the highest-priority determinant, emphasising governance capacity and structured execution; (3) significant trust deficits exist between developers and municipal authorities, undermining collaboration; (4) seniors prioritise design inclusivity and social integration, while developers emphasise cost efficiency and regulatory certainty; and (5) environmental sustainability consistently ranked lower (M ≈ 3.34) across all stakeholder groups due to pressing affordability concerns. Although municipal officers were intentionally oversampled (58%) due to their central role in Latvia’s housing governance, robustness checks confirmed the six-factor structure remained stable across stakeholder groups. This study contributes theoretically by contextualising adaptive reuse within shrinking cities and ageing societies and practically by providing a determinant-based framework for housing policy.