Forensic age estimation, a recent topic of research in forensic medicine, is of primary importance to criminal and civil law. Previous studies indicate that the observation of medial clavicular ossification allows for age discrimination along the completed 18th and 21st years of life. Experts recommend that the Schmeling and Kellinghaus methods be used together. In this study, we used these staging methods to retrospectively analyze 725 case studies (385 males, 340 females) of thin-slice computed tomography (CT) images, ranging from 0.6 to 1 mm in thickness, from individuals aged 10 to 35 years. Stage 1 was found at 18 years of age maximum for males, whereas it was found at 17 years of age for females. Stage 2a was found at 18 years of age maximum for both genders. Stage 3c was initially observed at 18 years for both genders. Stage 4 was initially found at 21 years for males and 20 years for females. Stage 5 was initially observed at 25 years for both genders. Of note, stage 3c was found close to 19 years of age for both genders (18.92 years for male, 18.99 years for female), and it may be employed to differentiate along the age majority cutoff. The data obtained from our study were consistent with previous studies. We believe that such a comprehensive database will greatly contribute to future studies focusing on medial clavicular ossification based on thin-slice CT. Moreover, we also recommend that if medial clavicular ossification based on CT is to be examined for forensic age estimation, both methods should be employed together.