Girl is initially nervous about old man's intentions (5)
I believe the answer is:
naomi
'girl' is the definition.
'initially nervous about old man's intentions' is the wordplay.
'initially' suggests taking the first letters.
The first letters of 'nervous about old man intentions' is 'NAOMI'.
'is' is the link.
(Other definitions for naomi that I've seen before include "Ruth's mother-in-law (OT)" , "Do I moan about Biblical Ruth's mother-in-law?" , "woman in the Bible" , "Mother-in-law of Ruth (Bible)" , "Biblical mother-in-law of Ruth" .)