Household in which people grow old (6)
I believe the answer is:
menage
'household' is the definition.
(eg menage a trois, literally a household of three)
'people grow old' is the wordplay.
'people' becomes 'men' (men are people).
'grow old' becomes 'age' (synonyms).
'men'+'age'='MENAGE'
'in which' is the link.
(Other definitions for menage that I've seen before include "Social unit living together" , "live together" , "Persons of household" , "a household, may be naughtily a trois" , "Members of a household" .)