Metacognition, or monitoring and controlling one’s knowledge, is a key feature of human cognition. Accumulating evidence shows that foundational forms of metacognition are already present in young infants and then scaffold later-emerging skills. While many animals exhibit cognitive processes relevant to metacognition, it is unclear if other species share the developmental trajectories found in human development. Here, we examine the emergence of metacognitive information-seeking in rhesus monkeys (Macaca mulatta). We presented a large sample of semi-free-ranging monkeys, ranging from juvenility to adulthood, with a one-shot task where they could seek information about a food reward by bending down to peer into a center vantage point in an array of tubes. In the hidden condition, information-seeking was necessary as no food was visible on the apparatus, whereas in the visible control condition information-seeking was not necessary to detect the location of the reward. Monkeys sought information at the center vantage point more often when it was necessary than in the control condition, and younger monkeys already showed competency similar to adults. We also tracked additional monkeys who voluntarily chose not to approach to assess monkeys’ ability to actively infer opportunities for information-seeking, and similarly found similar performance in juveniles and adults. Finally, we found that monkeys were overall slower to make metacognitive inferences than to approach known rewards, and that younger monkeys were specifically slower to detect opportunities for information-seeking compared to adults. These results indicate that many features of mature metacognition are already detectable in young monkeys, paralleling evidence for ‘core metacognition’ in infant humans.