Wild boar ultimately getting older (6)
I believe the answer is:
raging
'wild' is the definition.
(I know that wild can be written as raging)
'boar ultimately getting older' is the wordplay.
'ultimately' says to take the final letters.
'getting older' becomes 'aging' (I've seen this before).
The last letter of 'boar' is 'r'.
'r'+'aging'='RAGING'
(Other definitions for raging that I've seen before include "Furious, behaving violently" , "Extremely angry" , ". . . . . . Bull (Martin Scorsese film)" , "Showing violent anger" , "wild" .)