In becoming older, Lynn possibly getting mean (9)
I believe the answer is:
averaging
'getting mean' is the definition.
(I've seen this before)
'in becoming older lynn' is the wordplay.
I cannot really see how this works, but
'in' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'possibly' acts as a link.
Can you help me to learn more?
(Other definitions for averaging that I've seen before include "that has mean results" , "using statistical procedure" , "Taking a mean" , "Assessing the general quality" , "evening out" .)