age group

noun

persons of approximately the same age and often of the same sex, nationality, educational or social background, etc.

Origin of age group

First recorded in 1900–05

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

The age-group 15 to 20 shows very curious variations in the relative mortality of males and females.
Women in Modern Industry
B. L. Hutchins
Also disturbing are statistics showing that most of those apprehended for it are in the eighteen-to-thirty-year age-group.
Area Handbook for Bulgaria
Eugene K. Keefe, Violeta D. Baluyut, William Giloane, Anne K. Long, James M. Moore, and Neda A. Walpole

1904, originally a term in the science of demographics, from age (n.) + group (n.).