People can (to some extent) detect trustworthiness from the facial features of social partners, and populations which underperform at this task are at a greater risk of abuse. Here we focus on situations in which adolescents make a decision whether to trust an unknown adult. Adolescents aged 13–18 (N = 540) played a trust game, in which they made decisions whether to trust unknown adults based on their picture. We show that trusting decisions become increasingly accurate with age, from a small effect size at age 13 to an effect size 2.5 times larger at age 18. We consider the implications of this result for the development of prosociality and the possible mechanisms underlying the development of trustworthiness detection from faces.