Getting on a bit (4)
(Other definitions for aged that I've seen before include "Long in the tooth" , "Elderly" , "Old or ancient" , "Getting on" , "Senescent" .)
'getting on a bit?' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for elderly that I've seen before include "Silver" , "Past middle age, a senior citizen" , "... or not of tender years" , "Fairly old, past middle age" , "Not young" .)