Fully grown or ripe (6)
I believe the answer is:
mature
This clue is a double definition.
'fully grown' is the first definition.
(similar in meaning)
'ripe' is the second definition.
(I know that ripe can be written as mature)
(Other definitions for mature that I've seen before include "of older years" , "Full-grown - ripe" , "sensible" , "reach the end of term" , "Old film star" .)