Raillery is not good in older years (8)
I believe the answer is:
badinage
'raillery' is the definition.
(I know that badinage is a type of raillery)
'not good in older years' is the wordplay.
'not good' becomes 'bad' (bad is the opposite of good).
'older years' becomes 'age' (period of many years. I am not sure about the 'older' bit.).
'bad'+'in'+'age'='BADINAGE'
'is' is the link.
Can you help me to learn more?
(Other definitions for badinage that I've seen before include "Good-humoured banter (8)" , "Raillery, give-and-take" , "Teasing talk, banter" , "Humorous banter" , "Backchat, banter" .)