Ageing is characterized by progressive functional decline and increase in disease risk and imposes substantial burdens on human health. Identifying aging biomarkers in primates is crucial for advancing our understanding of human ageing and for informing interventions to mitigate age-related pathologies. However, a comprehensive grasp of these biomarkers is still lacking, hindering the translation of fundamental research into clinical practice. In this Review, we present the current knowledge on biomarkers of ageing at the cellular, tissue and organism levels in humans and non-human primates. Through systematic analysis of representative biomarkers across diverse biological contexts and scales, we discuss both the variability and the conservation of ageing-associated physiological changes, underscoring their importance in assessing and intervening in the ageing process. Finally, we critically assess challenges in ageing research and outline strategic avenues for future investigation.