It's certainly not helping mother, getting old (8)
I believe the answer is:
damaging
'it's certainly not helping' is the definition.
(something damaging is not helpful)
'mother getting old' is the wordplay.
'mother' becomes 'dam' (female parent of an animal).
'getting old' becomes 'aging' (I've seen this before).
'dam'+'aging'='DAMAGING'
(Other definitions for damaging that I've seen before include "Hurting" , "Causing harm or injury" , "injurious" .)