What is the age of the oldest active user that participated in the event held on 5/6/2016 at coordinates 121, 31?
oldest user refers to MAX(age); active user refers to is_active = 1; on 5/6/2016 refers to timestamp LIKE '2016-05-06%'; coordinates 121, 31 refers to longitude = 121 AND latitude = 31;
SELECT T3.age FROM app_events AS T1 INNER JOIN events_relevant AS T2 ON T1.event_id = T2.event_id INNER JOIN gender_age AS T3 ON T2.device_id = T3.device_id WHERE T1.is_active = 1 AND T2.longitude = 121 AND T2.latitude = 31 AND SUBSTR(T2.timestamp, 1, 10) = '2016-05-06' ORDER BY T3.age DESC LIMIT 1