CREATE TABLE captain (Captain_ID INT, Name TEXT, Ship_ID INT, age TEXT, Class TEXT, Rank TEXT)
CREATE TABLE Ship (Ship_ID INT, Name TEXT, Type TEXT, Built_Year FLOAT, Class TEXT, Flag TEXT)

What is the average age of captains in different classes?, and order mean age in asc order.
SELECT Class, AVG(age) FROM captain GROUP BY Class ORDER BY AVG(age)
SELECT "Class", AVG("age") FROM "captain" GROUP BY "Class" ORDER BY AVG("age") NULLS FIRST