Table schema:
CREATE TABLE volume (Weeks_on_Top INTEGER, Artist_ID VARCHAR); CREATE TABLE artist (Artist_ID VARCHAR, age VARCHAR)

Question: What is the average weeks on top of volumes associated with the artist aged 25 or younger?
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