Old criteria to be reworked by head of government (9)
I believe the answer is:
geriatric
'old' is the definition.
(I've seen this before)
'criteria to be reworked by head of government' is the wordplay.
'to be reworked' is an anagram indicator.
'by' means one lot of letters go next to another.
'head of' says to take the initial letters.
The first letter of 'government' is 'g'.
'criteria' is an anagram of 'eriatric'.
'eriatric' put after 'g' is 'GERIATRIC'.
(Other definitions for geriatric that I've seen before include "past it" , "Relating to old people" , "treatment of the elderly" , "Oldie" .)