Ageing English lord residing at first in cathedral city (7)
I believe the answer is:
elderly
'ageing' is the definition.
(thesaurus)
'english lord residing at first in cathedral city' is the wordplay.
'english' becomes 'e' (abbreviation).
'lord' becomes 'ld' (abbreviation for the aristocratic title).
'at first' indicates taking the first letters.
'in' is an insertion indicator.
'cathedral city' becomes 'ely' (I've seen this before).
The first letter of 'residing' is 'r'.
'r' placed within 'ely' is 'erly'.
'e'+'ld'+'erly'='ELDERLY'
(Other definitions for elderly that I've seen before include "over the hill" , "... or not of tender years" , "Rather old" , "Somewhat old" , "Quite old" .)