Cannabis use disorder commonly starts during adolescence or young adulthood but can occur at any age. The acceptability and availability of medical and recreational marijuana may influence its development, with increased onset among older adults. Cannabis use disorder typically progresses gradually over time, with increased frequency and quantity of cannabis use. Early onset of cannabis use, particularly before age 15, is a strong predictor of developing cannabis use disorder and other substance use and mental disorders in young adulthood. The perception of cannabis as less harmful than alcohol or tobacco has contributed to its increasing popularity among adolescents. The disorder is associated with risk-taking behaviors, conduct problems, and impairment in daily functioning. In adults, cannabis use disorder often involves daily cannabis use despite adverse consequences and unsuccessful attempts to quit. The rate of cannabis use among middle-aged and older adults is increasing, potentially influenced by availability and social acceptance, especially among the "baby boomer" generation.