Database: talkingdata
Question: What is the average age of the users who use model device of R7?
SQL: SELECT SUM(T1.age) / COUNT(T1.device_id) AS avg FROM gender_age AS T1 INNER JOIN phone_brand_device_model2 AS T2 ON T1.device_id = T2.device_id WHERE T2.device_model = 'R7'