Grave old yankee, one quiet and not conforming to a certain stereotype (9)
I believe the answer is:
tomboyish
'not conforming to a certain stereotype' is the definition.
(not conforming to gender stereotypes)
'grave old yankee one quiet' is the wordplay.
'grave' becomes 'tomb' (synonyms).
'old' becomes 'o' (abbreviation as in OT - Old Testament).
'yankee' becomes 'Y' (phonetic alphabet: alpha, bravo, charlie etc.).
'one' becomes 'i' (Roman numeral).
'quiet' becomes 'sh' ('sh' is used to tell someone to be quiet).
'tomb'+'o'+'y'+'i'+'sh'='TOMBOYISH'
'and' acts as a link.
(Another definition for tomboyish that I've seen is " like George in The Famous Five?".)