CREATE TABLE table_name_23 (age_as_of_1_february_2014 VARCHAR(255), province_or_country_of_birth VARCHAR(255))
What is the average age as of February 1, 2014 for the supercentenarians born in the United States?
    
SQL: SELECT age_as_of_1_february_2014 FROM table_name_23 WHERE province_or_country_of_birth = "united states"