Pretend to be a writer, young one imprisoned here? (7)
I believe the answer is:
playpen
'young one imprisoned here?' is the definition.
'pretend to be a writer' is the wordplay.
'pretend to be' becomes 'play'.
'a writer' becomes 'pen' (I've seen this before).
'play'+'pen'='PLAYPEN'
(Other definitions for playpen that I've seen before include "Nipper stuck here" , "juvenile restraint" , "Child's enclosure" , "Toddler's enclosure" , "Enclosure for child" .)