While anthropological scholarship on the life course transitions of young people has aimed to contribute to theories of structure and agency, social reproduction and change, it has done so relatively independently from the anthropological literature on subject formation. This paper explores how subjectivity – how people feel, think, and experience – is implicated in grappling with life course transitions. It addresses how ‘being serious’ is considered a critical adult competency and its achievement delineates a key life transition that young women in western Kenya variously resent and value, resist and seek. The analysis illuminates ways in which people grapple with their own subjectivity as a problem as well as a project, and how such problems and projects of subjectivity are problems and projects of social reproduction. I argue that taking account of such subjective transformations can augment political economy analysis of meanings and modes of life.