Active for one's age (4)
I believe the answer is:
spry
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">active for one's age</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for spry that I've seen before include "Light on one's feet" , "Still able to move lightly and fast" , "'Active and lively, nimble (4)'" , "Quick and agile" , "Agile (for one's age?)" .)