Pal grabbing university rector's top? Grow up! (6)
I believe the answer is:
mature
'grow up' is the definition.
(I've seen this before)
'pal grabbing university rector's top?' is the wordplay.
'pal' becomes 'mate' (I've seen this in other clues).
'grabbing' indicates putting letters inside.
'top?' says to take the initial letters (I've seen 'top' mean this).
The first letters of 'university rector' is 'ur'.
'mate' going around 'ur' is 'MATURE'.
(Other definitions for mature that I've seen before include "Ripe or fully grown" , "Grown-up" , "Fully grown and adult" , "Ripen or grow up" , "Age" .)