Sadly premature, accepting troop leader’s old hearing aid (3,7)
I believe the answer is:
ear trumpet
'old hearing aid' is the definition.
(I've seen this before)
'sadly premature accepting troop leader's' is the wordplay.
'sadly' is an anagram indicator.
'accepting' is an insertion indicator.
'leader' says to take the initial letters.
The first letter of 'troop' is 't'.
'premature' is an anagram of 'earrumpet'.
'earrumpet' placed around 't' is 'EAR-TRUMPET'.
(Other definitions for ear trumpet that I've seen before include "Former hearing aid" , "eight [HEARING AID]" , "sound engineering device" , "Primitive hearing aid" , "Old hearing aid" .)