Background: The Kilimanjaro region has one of the highest levels of reported alcohol intake per capita in Tanzania. Age at first drink has been found to be associated with alcohol problems in adulthood, but there is less information on the age of first drink in the Kilimanjaro region and its associations with alcohol-related consequences later in life. Furthermore, local alcohol cost and availability may influence the prevalence of alcohol use and alcohol use disorders. Methods: Data on the age of first drink, alcohol use disorder identification tool (AUDIT), number and type of alcohol consequences (DrInC), and perceived alcohol at low cost and high availability for children and adolescents were collected from an alcohol and health behavior survey of injury patients (N = 242) in Moshi, Tanzania. Generalized linear models were used to test age at first drink, perceived alcohol cost and availability, and their association with the AUDIT and DrInC scores, and current alcohol use, respectively. Results: Consuming alcohol before age 18 was significantly associated with higher AUDIT and DrInC scores, with odds ratios of 1.22 (CI: 1.004, 1.47) and 1.72 (CI: 1.11, 2.63), respectively. Female gender is strongly associated with less alcohol use and alcohol consequences, represented by an odds ratio of 3.70 (CI: 1.72, 8.33) for an AUDIT score above 8 and an odds ratio of 3.84 (CI: 2.13, 6.67) with the DrInC score. Perceived high availability of alcohol for children is significantly related to higher alcohol use quantity, with the odds ratio of 1.6 (CI: 1.17, 2.20). Conclusions: The first use of alcohol before the age of 18 is associated with higher alcohol use and alcohol-related adverse consequences. In Tanzania, age at first drink is an important target for interventions aiming to prevent negative alcohol-related consequences later in life.