<prompt> WHO defines adolescent age between :10-19 years of age10-14 years of age10-25 years of age9-14 years of age  <response>: WHO UN Definitions: Adolescent age 10-19years Youth - 15-24 years Young people - 10-24 years Ref: Ghai Essential Pediatrics By O. P. Ghai, Piyush Gupta, V. K. Paul, 6th Edition, Page 66; Cambridge Handbook of Psychology, Health and Medicine By Susan Ayers, Andrew Baum, Chris McManus, 2007, Page 5 