Novelist over fifty? Only just (6)
I believe the answer is:
hardly
'only just' is the definition.
(thesaurus)
'novelist over fifty?' is the wordplay.
'novelist' becomes 'hardy' (Hardy is a novelist).
'over' means one lot of letters goes inside another.
'fifty?' becomes 'l' (roman numeral).
'hardy' going around 'l' is 'HARDLY'.
(Other definitions for hardly that I've seen before include "Almost not" , "Not quite "It seems unlikely!"" , "Barely, scarcely" , "Not much" , "With great difficulty" .)