Pen life story about Romeo (4)
I believe the answer is:
biro
'pen' is the definition.
(Biro is an example)
'life story about romeo' is the wordplay.
'life story' becomes 'bio' (short for biography).
'about' means one lot of letters goes inside another.
'romeo' becomes 'r' (phonetic alphabet: alpha, bravo, charlie etc.).
'bio' placed around 'r' is 'BIRO'.
(Other definitions for biro that I've seen before include "Type of ballpoint pen" , "Lazlo -, ballpoint pen inventor" , "Writing implement" , "Laszlo Jozsef -, ballpoint pen inventor" , "writer" .)