Become mature (4,2)
(Other definitions for grow up that I've seen before include "Be your age, acquire maturity" , "Develop, become mature" , "Become mature, or an injunction to have sense" , "Become an adult" , "Become mature - or injunction to act like it?" .)
'become mature' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ripen that I've seen before include "Become ready for eating" , "Mature, develop" , "Grow older" , "Become ready to pick" , "Become ready to eat" .)
'become mature' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for age that I've seen before include "Very long time" , "Years lived so far" , "Period of time" , "Long period" , "16/18 [INDUSTRIAL REVOLUTION]" .)