This paper examines whether biological age, as distinct from chronological age, could become a new basis for discrimination. Drawing on Räsänen’s proposal that individuals be allowed to change their legal age to mitigate chronological age-based discrimination, it assesses whether this could introduce discrimination based on biological age. The analysis distinguishes chronological from biological age and clarifies differences. Chronological age measures the time elapsed since an entity’s existence, with unidirectional and perfect passage-of-time correlation. Biological age is the attempt to quantify the state of the ageing process—gradual deterioration of body and mind—via biomarkers compared with population averages. It is variable and potentially reversible. For these reasons, biological age currently is not familiar to the public; it lacks stability and institutional recognition and thus does not meet the conditions for discrimination as discussed by prominent theories of discrimination by Lippert-Rasmussen and Behrendt. Therefore, individuals are unlikely to face discrimination on this basis in the same sense as they might based on chronological age. However, if biological age were formally adopted—say, through legal reforms substituting or even replacing chronological age—it could acquire normative significance and potentially serve as a new basis for discrimination. Hence, openly available information about biological age should be limited to mitigate the risk that it could become a basis for discrimination.