Girl of four, starting young (3)
I believe the answer is:
ivy
'girl' is the definition.
(woman's name)
'four starting young' is the wordplay.
'four' becomes 'IV' (Roman numerals).
'starting' suggests taking the first letters.
The first letter of 'young' is 'y'.
'iv'+'y'='IVY'
'of' is the link.
(Other definitions for ivy that I've seen before include "Girl's name; climber" , "woman" , "Bush" , "Four-year" , "Poisonous plant" .)