The question ‘Who theorises age?’ is meant to draw attention to the everyday theorising about age and ageing engaged by ordinary men and women, which, it is argued, has striking parallels with the theoretical products of professional peers. Following a discussion of some phenomenological features of conventional theorising in the field of ageing, the process of ordinary theorising is illustrated from observational and narrative data gathered in a variety of human service institutions, home settings and small groups. Implications of the parallels for understanding the relation between ‘theory’ and ‘data’ are addressed and a programme suggested for linking ageing, gerontology, and the humanities.