Government staff get old chaps tense (10)
I believe the answer is:
management
'government' is the definition.
(management is a kind of government)
'staff get old chaps tense' is the wordplay.
'staff' becomes 'man' (manning is a kind of staffing).
'get old' becomes 'age' ('age' can be a synonym of 'get old').
'chaps' becomes 'men' (I've seen this before).
'tense' becomes 't' (abbreviation used in many dictionaries).
'man'+'age'+'men'+'t'='MANAGEMENT'
(Other definitions for management that I've seen before include "Organisation heads" , "Administration" , "Senior staff" , "board" , "The bosses" .)