Flying ace primed to live for the moment (5,4)
I believe the answer is:
carpe diem
'live for the moment' is the definition.
('carpe diem' is Latin for 'seize the day')
'flying ace primed' is the wordplay.
'flying' is an anagram indicator.
'ace'+'primed'='aceprimed'
'aceprimed' is an anagram of 'CARPE DIEM'.
'to' acts as a link.
(Other definitions for carpe diem that I've seen before include "Enjoy the moment! (Latin)" , "Seize occasion" , "from Horace" , "Make the most of the time you have" , "make the most of today" .)