Moving well for one's age (4)
I believe the answer is:
'moving well for one's age' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for spry that I've seen before include "Nimble (for one's age?)" , "Sprightly" , "Still able to move lightly and fast" , "'Agile, nimble (4)'" , "Nimble, brisk" .)