In this article, we investigate the accuracy of age reporting by people aged 60 and older and proxy reporting by their carers in a peri-urban area of Uganda, and analyse the factors that influence reporting by both groups. We find a high level of age heaping on terminal digits 0 and 5, indicating poor knowledge of age. Contrary to other studies, we find that literate people were more likely to exhibit age heaping. We link this to the absence of birth registration for this cohort and the introduction of National Identification (ID) cards in Uganda five years before our survey. We conclude that age heaping is better interpreted as an indicator of registration machinery than of human capital. We also find that the health, functional capabilities and education of older people influenced the age ascribed to them by their carers. Carers who knew the older people less well were more likely to overestimate their age, and carers of healthy and more educated people were more likely to report a younger age than that reported by the older people themselves. Where people don’t know their age, the age they report may also be influenced by their health and capabilities, making it difficult to establish true relationships between chronological age and outcomes such as health. In many disciplines, self-reported age or age reported by proxy respondents is accepted uncritically by researchers, but our study shows that in peri-urban Uganda age reporting remains approximate and biased, and this has strong implications for appropriate targeting and monitoring of interventions to support healthy ageing in such contexts.