Capacity to advance fast (6)
I believe the answer is:
talent
'capacity' is the definition.
(thesaurus)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for talent that I've seen before include "Attractive people" , "Special ability, flair" , "Natural ability or quality" , "Coin at one time" , "Gift - aptitude" .)