Dressing, group before getting on (9)
I believe the answer is:
Here is my best explanation:
'dressing' is the definition.
(bandaging is a kind of dressing)
'group before getting on' is the subsidiary indication.
'group' becomes 'band' (band is a kind of group**).
'before' is a charade indicator (letters next to each other).
'getting on' becomes 'aging' (I've seen this in other clues).