Apparatus, systems, and articles of manufacture are disclosed to categorize audience members by age. An example system includes a processor to execute instructions to: generate, an age-correction model by: at an initial node, splitting audience member records into child nodes based on an initial attribute-value pair; at the child nodes: calculating an effective quantity of audience member records based on the weight assigned to the corresponding child node; when the effective quantity of audience member records satisfies a minimum leaf size, splitting the corresponding child node into additional ones of the child nodes based on a corresponding child node attribute-value pair; and when the effective quantity of audience member records does not satisfy the minimum leaf size, designating the corresponding child node as a terminal node; and correct, based on the age-correction model, an age characteristic associated with a media impression.