This paper examines how young people account for choosing mathematical subjects, and how these processes sustain, or not, their continued participation. It draws on a 2-year qualitative study of 24 young people's accounts of following advanced mathematical pathways within a widening participation programme. Working within a post-structural framework, I combine two arguments: firstly, that local discourses of time, age and maturity position contemporary adolescence as a time of 'becoming' that aligns personal aspirations with mathematical progress, and secondly that students' accounts of choice and aspiration require multiple imaginings of present and future selves. I identify distinct discourses -- "moving/improving" and "getting ahead" -- that structure the intelligibility of participation in mathematics and further mathematics respectively. I argue that tracing the alignments between students' accounts of themselves and/ in mathematics offers potential to understand emergent practices in mathematics participation but also how exclusions are re-inscribed along classed and gendered lines.