Maybe easons puts Harry potter books in the young adult section but young adult is around 18-30 outside of entertainment categories
https://en.m.wikipedia.org/wiki/Young_adult_(psychology)
A young adult is generally a person ranging in age from their late teens or early twenties to their thirties, although definitions and opinions
https://en.m.wikipedia.org/wiki/Erikson%27s_stages_of_psychosocial_development
Adolescence: 12-19 years Early adulthood: 19-35 years
https://www.census.gov/content/dam/Census/library/publications/2017/demo/p20-579.pdf
This report looks at a snapshot of the young adult population, defined here as 18 to 34 years old