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 table_name_6 (year_of_marriage INTEGER, her_age VARCHAR, his_age VARCHAR)

### Question ###
What is the mean year of marriage when her age was more than 19 and his age was 30?

### Accurate SQL ###

SELECT AVG(year_of_marriage) FROM table_name_6 WHERE her_age > 19 AND his_age = 30