Historically, age has been and still is a major organizing principle for social relations and the allotment of resources and power, yet age is very seldom acknowledged as a social categorization in its own right and in intersection with other identity categorizations. While feminist scholarship and activism have deconstructed racist and sexist discourses, in which biology is often used to legitimize social injustice, the presupposed naturalness of ageism is rarely challenged. The aim of the present paper is to explore if and why age relations and ageism are invisible in feminist work by interviewing eleven feminists in a Swedish context. The interviews, which are qualitative and semi-structured, have been thematically analysed to identify patterns in the respondents’ approaches to age as a social categorization in intersectional analysis. A recurring theme is explaining age and ageism in terms of a fluidity of age relations, which make it a complex categorization to include in intersectional analysis. Drawing on theories of ageing and intersectional feminism I explore how the research material can be understood from a social and historical perspective. The thesis builds on a post-constructionist epistemology which underlines the importance of situated knowledges and accountability, and I therefore chose to make myself as the author visible throughout the text by writing the I and including personal accounts related to ageism and ageing.