Both Uses of

provincial

in

The Great Gatsby

But young men didn't — at least in my provincial inexperience I believed they didn't — drift coolly out of nowhere and buy a palace on Long Island Sound.
p. 49.4 *

provincial = unsophisticated

Then he went into the jewelry store to buy a pearl necklace — or perhaps only a pair of cuff buttons — rid of my provincial squeamishness forever.
p. 179.4

Definitions:

(1) (provincial as in: provincial attitude)
unsophisticated (meant disapprovingly to refer to old-fashioned or narrow-minded attitudes and ideas)
(2) (meaning too rare to warrant focus)
Provincial can also mean "related to a province" or "related to the provinces." Its more literary meaning of unsophisticated originated as a pejorative term for ideas held in the provinces that were considered old-fashioned or uninformed by many who lived in the capital city.