In an immersive virtual reality (IVR) environment, this study investigated: (1) the role of learner characteristics in various learning and psychological outcomes, including knowledge retention, perceived learning, cognitive load, self-efficacy, enjoyment, presence, and usefulness; and (2) the relationship among these intended outcomes. Forty adult participants experienced an IVR nature trail tour involving science learning topics, followed by a knowledge test and multiple surveys. Multivariate analysis of covariance results indicated age by gender interaction effects on perceived presence and usefulness as well as an age by IVR prior experience interaction effect on perceived presence. Additionally, multiple correlational relationships were detected among the intended outcomes. This study contributes to the limited research on the role of learner characteristics in STEM learning and psychological outcomes in IVR environments.