Encourage, for example, middle-age! (3)
I believe the answer is:
egg
'encourage' is the definition.
'example middle-age' is the wordplay.
'example' becomes 'eg'.
'middle' indicates the central letters.
The middle letter of 'age' is 'g'.
'eg'+'g'='EGG'
'for' is the link.
(Other definitions for egg that I've seen before include "Baby carrier?" , "start in life" , "Breakfast food, perhaps" , "Good, boiled, yoke or head" , "Reproductive unit" .)