Adolescent initially needs support earlier on (4)
I believe the answer is:
teen
'adolescent' is the definition.
(I've seen this before)
'initially needs support earlier on' is the wordplay.
'initially' indicates taking the first letters.
'support' becomes 'tee' (tee is a kind of support).
'earlier on' means one lot of letters go next to another.
The first letter of 'needs' is 'n'.
'n' after 'tee' is 'TEEN'.
(Other definitions for teen that I've seen before include "Of 13 to 19 year olds" , "Adolescent (informal)" , "Youth" , "Youngster of a certain age" , "Young person" .)