Tree much more mature than those in nursery? (5)
I believe the answer is:
elder
'tree' is the definition.
(elder is a kind of tree)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for elder that I've seen before include "Patriarch" , "Tree - wise counsellor" , "Church official; tree" , "Shrub - church official" , "Senior tribal figure" .)