Agile learner lives a bit (7)
I believe the answer is:
lissome
'agile' is the definition.
(I've seen this in another clue)
'learner lives a bit' is the wordplay.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'lives' becomes 'is' ('be' can be a synonym of 'live').
'a bit' becomes 'some' (I've seen this in another clue).
'l'+'is'+'some'='LISSOME'
(Other definitions for lissome that I've seen before include "Lithe; nimble" , "So smile, being agile and lithe" , "Moving supply" , "Willowy" , "flexible" .)