An increase in irregular migration flows has further raised the importance of age estimation in forensic science. To improve the reliability of age of majority determination, one recommendation is to combine the evaluation of third molar development with age-related skeletal information. In the present study, we assessed mandibular third molar development and cervical vertebral maturation to evaluate the ability of these age indicators, alone and in combination, to accurately identify individuals 18 years of age or older. The study sample comprised 123 multi-slice computed tomography images of Mexican individuals (67 males and 56 females) aged between 14 and 22 years. Demirjian's stages of tooth development and Baccetti's stages of vertebral maturation were used. A fully developed mandibular third molar (stage H) indicated adult age with 100% certainty. However, around 70% of individuals older than 18 years had third molars that had not yet completed their development. Thus, immature third molars do not rule out the possibility that an individual has reached the age of majority. In the study sample, the combination of the maturity stages of teeth 38 and 48 or their combination with the cervical stages of maturation did not improve upon the prediction accuracy of either of the mandibular third molars alone (area under the ROC curve >
0.85). Therefore, these findings highlight the need to identify other complementary age estimation methods that minimize the number of false negatives (i.e., adults classified as minors) obtained with assessment of third molar development alone.