The COVID-19 pandemic profoundly disrupted the lives of older adults, yet their experiences have remained underexplored. This paper draws on empirical evidence from a two-wave (W1 April-July 2020, W2 January-April 2021) qualitative study in the UK (n=62) and a companion study in Colombia (n=32), focusing on participants aged 60 and above. Data was analysed using constructivist grounded theory principles, leading to the development of an ecological theory of older adults' well-being at three interconnected levels: individual, community, and societal. Individual resources, such as adaptability and support systems, contributed to enhancing and maintaining their well-being. Community support and a sense of belonging were essential to meet the needs of people in later life, whilst necessary social health protection measures during the pandemic restricted social activities, further impacting well-being, mostly perceived as challenging. Cultural differences and societal support systems shaped participants' experiences. The study emphasises the interdependence of the different levels in impacting older adults' well-being, offers strategies for policy and practice, and advocates and contributes for the development of gerontological theories in the context of health crises.