The notion of the heterogeneity of aging goes along with the awareness that every person experiences aging differently. Over the past years, scholars have emphasized that the assessment of these subjective experiences of aging contributes to our understanding of a range of psychological and physiological processes and outcomes among older adults. One construct frequently used in this context is subjective age, that is, how old or young a person feels. Subjective age has been shown to be an important correlate as well as a predictor of markers of successful aging such as well-being, health, and longevity. However, less is known about the antecedents of subjective age and the mechanisms underlying the relationship between feeling younger and positive developmental outcomes. This article briefly summarizes and critically evaluates the empirical evidence on this topic and makes suggestions on how to address and potentially overcome currently existing theoretical, methodological, and psychometric challenges. Based on the discussion of these challenges, the paper provides directions for future research by outlining underexplored topics such as intraindividual variability and determinants of subjective age, the match between objective age indicators and subjective age, and how subjective age maps on behavior and functioning.