Grow old (3)
'grow old' is the definition.
(synonyms)
This is all the clue.
(Other definitions for age that I've seen before include "Years since birth" , "Mature, grow in years" , "Period of time" , "Long period" , "16/18 [INDUSTRIAL REVOLUTION]" .)
'grow old' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for get on that I've seen before include "Make progress or mount up" , "Make progress or advance in age" , "Age; prosper" , "Board - prosper" , "Make progress or climb aboard" .)