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 music_festival ( id number, music_festival text, date_of_ceremony text, category text, volume number, result text )
TABLE: CREATE TABLE artist ( artist_id number, artist text, age number, famous_title text, famous_release_date text )
TABLE: CREATE TABLE volume ( volume_id number, volume_issue text, issue_date text, weeks_on_top number, song text, artist_id number )

### Question ###
Return the average number of weeks on top for volumes by artists that are at most 25 years old.

### Accurate SQL ###

SELECT AVG(T2.weeks_on_top) FROM artist AS T1 JOIN volume AS T2 ON T1.artist_id = T2.artist_id WHERE T1.age <= 25