Caged animals finding endless grief after people grow old (9)
I believe the answer is:
menagerie
'caged animals' is the definition.
(a menagerie is a collection of animals)
'endless grief after people grow old' is the wordplay.
'endless' means to look at the middle letters.
'after' means one lot of letters go next to another.
'people' becomes 'men' (men can refer to humanity as a whole).
'grow old' becomes 'age' (synonyms).
The centre of 'grief' is 'rie'.
'men'+'age'='menage'
'rie' put after 'menage' is 'MENAGERIE'.
'finding' acts as a link.
(Other definitions for menagerie that I've seen before include "Zoo" , "[TENNESSEE WILLIAMS] work in part" , "Beastly lot" , "A collection of wild animals in captivity" , "collected animals" .)