The sociology of old age has treated the final stage of the life course as a ‘residual category’ having little autonomy from the structuring processes of modernist institutions and individual biographies. In recent decades, this view has been challenged by the emergence of the third age. Less attention has been paid to theorizing its mirror image, the ‘fourth age.’ We argue that the fourth age acts as a ‘social imaginary’ of a feared old age, affecting the young as well as the retired. We call for further study of this fourth age imaginary as a distinct, sociological phenomenon.