Mature pine lasting many years (3-4)
I believe the answer is:
age-long
'lasting many years' is the definition.
'age-long' can be an answer for 'lasting' (thesaurus). I am not sure about the 'many years' bit.
'mature pine' is the wordplay.
'mature' becomes 'age' (synonyms).
'pine' becomes 'long' (to pine for something is to long for it).
'age'+'long'='AGE-LONG'
Can you help me to learn more?
(Other definitions for age-long that I've seen before include "Having existed for many a year" , "Seeming to have always been so" .)