Forensic age estimation of a living individual is frequently performed in clinical forensic medicine. Medicolegal physicians are usually called upon by the authorities to estimate the age of a living person requesting asylum or to determine whether a suspected offender is subject to juvenile or adult criminal law. Dental age is one of the parameters studied to estimate biological age. Several methods are used, and among these, analysis of the eruption of the third molar (M3) on an orthopantomogram (OPG) is one of the common methods. The objective of the study was to analyse the contribution of M3 eruption to age estimation, in particular with regard to the threshold of 18 years of age, in a sample of individuals examined in a French university hospital. The stage of wisdom tooth eruption of all individuals aged between 15 and 24 years, who had an OPG performed between 1 January 2013 and 31 December 2015, was interpreted using a three-stage scoring system. In total, 557 OPGs (340 males and 217 females) were included. None of the stage scores allowed a distinction between minors and majors, for either sex. Overall, 85% of females and 98% of males with four M3s in stage 3 (complete emergence in the occlusal plane) were majors.