Working in mine with all ages (9)
I believe the answer is:
millennia
'ages' is the definition.
(I've seen this before)
'working in mine with all' is the wordplay.
'working' indicates anagramming the letters.
'with' means one lot of letters go next to another.
'in'+'mine'='inmine'
'inmine' put after 'all' is 'allinmine'.
'allinmine' with letters rearranged gives 'MILLENNIA'.
(Other definitions for millennia that I've seen before include "Thousand-year periods" , "Could seem an interminable time" , "Spans of 1,000 years" , "Thousand year periods" , "Thousands of years" .)