Perceptions of age influence how we evaluate, approach, and interact with other people. Based on a paramorphic human judgment model, the present study investigates possible determinants of accuracy and bias in age estimation across the adult life span. For this purpose, 154 young, middle-aged, and older participants of both genders estimated the age of 171 faces of young, middle-aged, and older men and women, portrayed on a total of 2,052 photographs. Each face displayed either an angry, fearful, disgusted, happy, sad, or neutral expression (FACES database; Ebner, Riediger, & Lindenberger, 2010). We found that age estimation ability decreased with age. Older and young adults, however, were more accurate and less biased in estimating the age of members of their own as compared with those of the other age group. In contrast, no reliable own-gender advantage was observed. Generally, the age of older faces was more difficult to estimate than the age of younger faces. Furthermore, facial expressions had a substantial impact on accuracy and bias of age estimation. Relative to other facial expressions, the age of neutral faces was estimated most accurately, while the age of faces displaying happy expressions was most likely underestimated. Results are discussed in terms of methodological and practical implications for research on age estimation.