Old soldier's aspiration, inflamed within (7)
I believe the answer is:
hoplite
'old soldier's' is the definition.
(I've seen this before)
'aspiration inflamed within' is the wordplay.
'aspiration' becomes 'hope' (I've seen this in another clue).
'inflamed' becomes 'lit' (I've seen this in another clue).
'within' is an insertion indicator.
'hope' enclosing 'lit' is 'HOPLITE'.
(Other definitions for hoplite that I've seen before include "Foot-soldier" , "Old soldier" , "Infantryman" .)