Ace, old and bold! (6)
I believe the answer is:
expert
'ace' is the definition.
(both can mean a master of something)
'old and bold' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'and' means one lot of letters go next to another.
'bold' becomes 'pert' (I've seen this in another clue).
'ex'+'pert'='EXPERT'
(Other definitions for expert that I've seen before include "At the right moment" , "Master" , "One has specialist knowledge or ability" , "Having specialised knowledge" , "Specialist, pundit" .)