The following study investigates the dynamics of human-robot interaction (HRI) by examining how a robot’s behavior (fair vs. unfair) and its perceived age (adult vs. child) influence the attribution of mental states and moral judgment in a competitive game. Using an immersive virtual reality environment, a between-subjects design was employed in which participants interacted with a robot under four different conditions, manipulating the robot’s behavior and perceived age. Participants’ psychological and social responses were assessed through questionnaires. Results indicate that perceived age affects responsibility and intentionality attributions, with younger robots judged less morally accountable. Additionally, unfair behavior reduces trust and likability, decreasing the interaction enjoyment. These findings emphasize the importance of designing social robots that behave in ways that are morally aligned with human expectations to foster trust and cooperation.