I see your point, re-reading your original post. The phrase "young culture", to me, carries a heavy emphasis of literal age. Ultimately -- and semantic quibbli

I see your point, re-reading your original post. The phrase "young culture", to me, carries a heavy emphasis of literal age. Ultimately -- and semantic quibbling aside -- I think you're right that American culture is (and by extension, typical Americans are) particularly energetic and optimistic. I'm not sure I agree with unsophisticated, unless you mean "less formal".