Highest point for one turning into adult writer (6)
I believe the answer is:
apogee
'highest point' is the definition.
(I've seen this before)
'one turning into adult writer' is the wordplay.
'one turning' becomes 'ge' (I can't justify this - if you can you should believe this answer much more).
'into' is an insertion indicator.
'adult' becomes 'a' (abbreviation).
'writer' becomes 'Poe' (Edgar Allan Poe).
'a'+'poe'='apoe'
'ge' inserted within 'apoe' is 'APOGEE'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for apogee that I've seen before include "Highest point (of orbit)" , "Outermost orbital point" , "Apex, peak" , "highly significant point" , "Satellite's furthest point" .)