Young people (9)
I believe the answer is:
teenagers
'young people' is the definition.
(people aged between twelve and twenty)
This is the entire clue.
(Other definitions for teenagers that I've seen before include "They're between the onset of puberty and maturity, generally" , "Adolescents" , "Young people" , "They're aged between 13 and 19" , "Youngsters" .)