Reach adult status (4,2,3)
I believe the answer is:
come of age
'reach adult status' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for come of age that I've seen before include "Reach maturity with rights to vote etc" , "Reach adulthood" , "Reach full adult status" , "Reach adult status, perhaps 21" , "Attain maturity" .)