The volatile opioid epidemic is associated with higher levels of opioid use disorder (OUD) and negative health outcomes in adolescents and young adults. Medications for opioid use disorder (MOUD) demonstrate the best evidence for treating OUD. Adherence to and retention in MOUD among adolescents and young adults, however, is incompletely understood. This systematic review examines the state of the literature regarding the association of age with adherence to and retention in MOUD using methadone, buprenorphine, or naltrexone among persons aged 10 to 24 along with related facilitators and barriers. The research team searched for all studies of MOUD that examined adherence, retention, or related concepts as an outcome variable where the sample included adolescents or young adults. Search criteria generated 10,229 records, which, after removing duplicates and conducting title/abstract screening, yielded 587 studies for full-text review. Ultimately, 52 articles met inclusion criteria for abstraction and 17 were selected for qualitative coding and analysis. This review found younger age to be consistently associated with shorter retention in the published literature, although the overall quality of included studies was low. Several factors at the individual, interpersonal, and institutional levels, such as concurrent substance use, MOUD adherence, family conflict, and MOUD dosage and flexibility, were seen as playing a role in MOUD retention among adolescents and young adults. This review highlights how MOUD providers can tailor treatment to increase retention of adolescents and young adults while pointing to the need for more research explaining MOUD adherence and retention disparities in this age group.