In March 2020, the government of the United Kingdom advised all people aged 70 and above to self-isolate stringently for a minimum of 12 weeks in response to COVID-19. The British Society of Gerontology criticised the government for ignoring individual differences, deeming the approach ageist. Former British Geriatrics Society president David Oliver contested accusations of ageism, arguing that the approach was pragmatic discrimination based on epidemiological evidence. This debate catalyses core gerontological tensions regarding ageism, discrimination, categorisation and heterogeneity. A critical realist perspective reveals that both the government and gerontology are struggling to negotiate these irresolvable tensions. Contrary to the binary debate, age-based isolation simultaneously represents pragmatic discrimination and value-driven ageism. However, it does so partly because it relies on a chronologic epistemology that positions age as a potent biosocial axis of meaningful difference, thereby reflecting gerontology’s own ageism. The ethical purism of gerontological accusations of ageism is thus somewhat misplaced, potentially obscuring an opportunity for reflection on value-laden engagements with age in social research.