Active ageing is a policy tool that dominates the way the ageing society has been constituted during the last decades. The authors argue that active ageing is an attempt at unmaking the concept of old age, by engaging in the plasticity of ageing in various ways. Through a document study of the different epistemes, models and forms used in the constitution of active ageing policies, the authors show how active ageing is not one coordinated set of policy instruments, but comes in different formats. In the WHO, active ageing configures individual lifestyle in order to expand the plasticity of ageing, based on epidemiological and public health conventions. In the EU, active ageing reforms the retirement behaviour of populations in order to integrate the plasticity of ageing into the institutions, based on social gerontological and demographic conventions. These conventional arrangements are cognitive and political in the way they aim at unmaking both the structures and the expectations that has made old age and format a new ideal of the 'good late life'. The paper examines the role of knowledge in policy and questions whether the formats of active ageing should be made to co-exist, or whether the diversity and comprehensiveness enable a local adaptation and translation of active ageing policies.