What is the average age as of February 1, 2014 for the supercentenarians born in the United States?
CREATE TABLE "living_canadian_supercentenarians" (
  "name" text,
  "birth_date" text,
  "age_as_of_1_february_2014" text,
  "province_or_country_of_birth" text,
  "province_of_residence" text
);
SELECT "age_as_of_1_february_2014" FROM "living_canadian_supercentenarians" WHERE "province_or_country_of_birth"='united states';