Aging is a ubiquitous component of the life history and biological function of all species. In wildlife studies, estimates of age are critical in order to understand how a species’ ecology, biology and behaviour vary in parallel with its life-history events. Longitudinal studies that track individuals as they age are limited in fruit bats, as recapture is difficult for vagile species with nomadic lifestyles. Most studies estimate age by the broad categorisation of individuals with similar biological characteristics or morphometrics into age classes (e.g. sub-adult and adult). In this review, we systematically compile and compare the age classifications used across a range of studies on Australian flying-foxes (Pteropus). We discuss the associated challenges of those classifications and identify current knowledge gaps. The terminology, methodology and explanations behind age classifications were inconsistent across reviewed studies, demonstrating that age classifications are highly subjective – particularly when identifying reproductively immature individuals. Downstream analyses and cross-disciplinary data use are likely to be compromised as a result. Further known-aged studies of flying-foxes would assist in clarifying variations of key parameters among non-adult individuals. We also encourage greater consistency in age classification and reporting, ensuring that classifications are well defined and biologically sound.