Fun to carry on with golf in old age (9)
I believe the answer is:
longevity
'old age' is the definition.
(thesaurus)
'fun to carry on with golf' is the wordplay.
'fun' becomes 'levity' (I am not sure about this - if you are sure you should believe this answer much more).
'to carry' is an insertion indicator.
'with' is a charade indicator (letters next to each other).
'golf' becomes 'g' (phonetic alphabet: alpha, bravo, charlie etc.).
'on'+'g'='ong'
'levity' placed around 'ong' is 'LONGEVITY'.
'in' is the link.
Can you help me to learn more?
(Other definitions for longevity that I've seen before include "sustained survival?" , "Lengthy life" , ""Length of days"" , "far from short life" , "endurance" .)