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 student (stuid VARCHAR, age INTEGER)
TABLE: CREATE TABLE has_pet (stuid VARCHAR)

### Question ###
Find number of pets owned by students who are older than 20.

### Accurate SQL ###

SELECT COUNT(*) FROM student AS T1 JOIN has_pet AS T2 ON T1.stuid = T2.stuid WHERE T1.age > 20