Old nurse close to commode encountering aroma that's characteristic of old age (9)
I believe the answer is:
senescent
'characteristic of old age' is the definition.
(I've seen this before)
'old nurse close to commode encountering aroma' is the wordplay.
'old nurse' becomes 'SEN' (state-enrolled nurse).
'close to' says to take the final letters (the close/ending of).
'encountering' says to put letters next to each other.
'aroma' becomes 'scent' (synonyms).
The final letter of 'commode' is 'e'.
'sen'+'e'+'scent'='SENESCENT'
'that's' is the link.
(Other definitions for senescent that I've seen before include "Showing signs of age" , "Getting old" , "characteristic of old age" , "Ageing" , "Showing age-related deterioration" .)