Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE student (age INTEGER, stuid VARCHAR); CREATE TABLE has_pet (age INTEGER, stuid VARCHAR)
### Question:
Find the average age of students who do not have any pet .
### Answer:
SELECT AVG(age) FROM student WHERE NOT stuid IN (SELECT stuid FROM has_pet)