This research examined how 5-, 8-, and 11-month-olds with female primary caregivers mentally represented faces using a familiarization procedure similar to real-world experience in which infants have greater exposure to female faces aged 21-39 years than other face types. We predicted infants would form weighted representations of faces (i.e., representations weighted toward the most frequently seen faces) and would more easily form weighted representations of female than male faces given their predominant experience with women (Experiments 1 and 2). We also tested adults using this familiarization procedure (Experiment 3) and predicted they would form averaged representations of faces based on data showing that preferences for averageness (the mathematical central tendency of a population) get stronger with development. Data from the three studies supported these hypotheses. Differences in how infants and adults mentally represent faces might be developmentally advantageous and such representations provide a mechanism to help explain the differential expertise in infants' and adults' face processing abilities.