Some young people finally drown in river (5)
I believe the answer is:
teens
'some young people' is the definition.
(I've seen this in another clue)
'finally drown in river' is the wordplay.
'finally' says to take the final letters.
'in' indicates putting letters inside.
'river' becomes 'tees' (River Tees).
The last letter of 'drown' is 'n'.
'n' placed within 'tees' is 'TEENS'.
(Other definitions for teens that I've seen before include "Adolescent years" , "Years 13-19" , "Between 12 and 20" , "Adolescence" , "seven-year period" .)