Star, very mature, making a comeback (4)
I believe the answer is:
vega
'star' is the definition.
(Vega is an example)
'very mature making a comeback' is the wordplay.
'very' becomes 'v' (abbreviation).
'mature' becomes 'age' ('age' can be a synonym of 'mature').
'making a comeback' shows that the letters should be reversed in order.
'age' reversed gives 'ega'.
'v'+'ega'='VEGA'
(Other definitions for vega that I've seen before include "Gave turn to a star" , "Brightest star of constellation Lyra" , "Fifth brightest star" , "Bright star of constellation Lyra" , "First magnitude star" .)