Adolescent requiring support with last bit of revision (4)
I believe the answer is:
teen
'adolescent' is the definition.
(teenager)
'support with last bit of revision' is the wordplay.
'support' becomes 'tee' (tee is a kind of support).
'with' is a charade indicator (letters next to each other).
'last bit of' says to take the final letters.
The final letter of 'revision' is 'n'.
'tee'+'n'='TEEN'
'requiring' is the link.
(Other definitions for teen that I've seen before include "Young person" , "Youngster of a certain age" , "Youngster over twelve" , "Adolescent (informal)" , "Youth" .)