Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE captain ( Captain_ID int, Name text, Ship_ID int, age text, Class text, Rank text )
TABLE: CREATE TABLE Ship ( Ship_ID int, Name text, Type text, Built_Year real, Class text, Flag text )

### Question ###
Return the average age of captains in each class.

### Accurate SQL ###

SELECT Class, AVG(age) FROM captain GROUP BY Class