DEAR DR. BLONZ: At what age is a person considered an adult as regards nutrient requirements? : The answer of when to grant “adult” status for nutrient levels varies based on a number of factors. At some time during the adolescent years, ages 13 through 17, the child transitions into their adult body. Some medications direct you to use adult dosing from age 12 on, while other medicines have separate guidelines up to age 18. Keep in mind that the example you and other adults set is the seed that takes root as your daughter transitions to adulthood.