Girl has old aim (4)
I believe the answer is:
goal
'aim' is the definition.
(I've seen this before)
'girl has old' is the wordplay.
I cannot really understand how this works, but
'girl' could be 'g' and 'g' is present in the answer.
'old' could be 'o' (common abbreviation eg in OE for Old English) and 'o' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for goal that I've seen before include "Aim - two posts, a crossbar and a net" , "Footballer's target" , "could be worth 3 points" , "posts and bar" , "A score in soccer" .)