Service and maturity - there's the rub! (7)
I believe the answer is:
massage
'the rub' is the definition.
(thesaurus)
'service and maturity' is the wordplay.
'service' becomes 'mass' (I've seen this in other clues**).
'and' means one lot of letters go next to another.
'maturity' becomes 'age' (I've seen this before).
'mass'+'age'='MASSAGE'
'there's' is the link.
(Other definitions for massage that I've seen before include "Manipulation of the muscles" , "Relaxing manipulation" , "Present favourably" , "Knead" , "Manipulate the muscles" .)