Parson, surprisingly old for a singer (7)
I believe the answer is:
soprano
'a singer' is the definition.
(soprano is a kind of singer)
'parson surprisingly old' is the wordplay.
'surprisingly' indicates an anagram.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'parson' is an anagram of 'sopran'.
'sopran'+'o'='SOPRANO'
'for' acts as a link.
(Other definitions for soprano that I've seen before include "Producer of high-pitched sounds" , "High singing voice" , "Singer who aims high" , "chorus girl, perhaps" , "Norman, perhaps" .)