Destruction of age-old Northern Irish location (7)
I believe the answer is:
donegal
'irish location' is the definition.
(I know this)
'destruction of age-old northern' is the wordplay.
'destruction of' is an anagram indicator.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'age'+'old'+'n'='ageoldn'
'ageoldn' anagrammed gives 'DONEGAL'.
(Other definitions for donegal that I've seen before include "Ireland's northmost county" , "Northernmost Irish county" , "Irish town" , "town and county" , "part of Ireland" .)