In this paper we consider some of the ways that the third age can be thought about and studied. Taking the work of Peter Laslett as our key source, we explore his ‘aspirational’ approach toward redefining post-working life and look at some of its limitations as both definition and explanation. There is a need for a more sociologically informed approach to the third age, and we outline three potentially important structures that might better explain it – class, birth cohort, and generation. Whilst it might seem attractive to see the third age as a class-determined status, based on the material and social advantages accruing to people who have retired from well-paid positions in society, the historical period in which the third age has emerged makes this explanation less than adequate. Equally a cohort-based explanation, locating the third age in the ‘ageing’ of the birth cohort known as the baby boom generation, fails fully to capture the pervasiveness and irreversibility of the cultural change that has shaped not just one but a sequence of cohorts beginning with those born in the years just before World War II. Instead, we argue for a generational framework in understanding the third age, drawing upon Mannheim rather than Marx as the more promising guide in this area.