Worried little one is among the elderly (8)
I believe the answer is:
agonised
'worried' is the definition.
(to agonise is to worry or fret)
'little one is among the elderly' is the wordplay.
'little' means to remove the last letter (the word is not quite complete).
'among' is an insertion indicator (inserted letters are placed among others).
'the elderly' becomes 'aged' (I've seen this before).
'one' with its final letter removed is 'on'.
'on'+'is'='onis'
'onis' placed into 'aged' is 'AGONISED'.
(Other definitions for agonised that I've seen before include "Was in great doubt" , "Did Labour" , "Underwent mental anguish (over something)" , "experienced pain" , "Suffered mentally in San Diego" .)