Forensic studies on frontal sinus identification are often limited to adult samples or utilize static, simulated antemortem images, which overlook any potential temporal changes in sinus morphology. Further, studies on frontal sinus growth typically utilize lateral radiographs and/or are cross-sectional. The current study utilizes a longitudinal sample of frontal radiographs to determine the age at which forensically relevant frontal sinus traits stabilize during growth and development. The sample includes 1500 radiographs of 141 individuals (66F/75M) ranging from three to 56 years of age (yoa). For each individual, trait age-of-stabilization was recorded by identifying the year at which each coded trait became consistent across images.Our results demonstrate that frontal sinus traits stabilize on average 10–15yoa, with sinus presence being the first to stabilize and arcade counts the last. Females generally stabilized earlier (9–14yoa) versus males (10–15yoa). However, sex differences were generallynot statistically significant. Further, traits displayed a high degree of variation with wide standard deviations (~3 years). However, by 21yoa almost all individuals displayed stabilization in all traits, suggesting that little change should be expected with later-aged postmortem radiographs. Still, given the amount of variation, forensic practitioners should be cautious using frontal sinus identification methods in subadults, especially when years may have elapsed between images. When conducting a radiographic comparison that involves a subadult antemortem image, the results of this study may help the practitioner interpret whether the differences between antemortem and postmortem radiographs can be explained by age and time elapsed between radiographs.