Compute the average time in minute for each age group
teenager refers to 13 < age < = 19; adult refers to 19 < age < = 65; elder refers to age < = 65; highest average time per complaint = max(divide(sum(ser_time), count(ser_time)))
SELECT CAST(SUM(CASE WHEN T1.age > 13 AND T1.age <= 19 THEN 60 * strftime('%H', ser_time) + strftime('%M', ser_time) + strftime('%S', ser_time) / 60 ELSE 0 END) AS REAL) / SUM(CASE WHEN T1.age > 13 AND T1.age <= 19 THEN 1 ELSE 0 END) AS teenagerAverageMins, CAST(SUM(CASE WHEN T1.age > 19 AND T1.age <= 65 THEN 60 * strftime('%H', ser_time) + strftime('%M', ser_time) + strftime('%S', ser_time) / 60 ELSE 0 END) AS REAL) / SUM(CASE WHEN T1.age > 19 AND T1.age <= 65 THEN 1 ELSE 0 END) AS adultAverageMins , CAST(SUM(CASE WHEN T1.age > 65 THEN 60 * strftime('%H', ser_time) + strftime('%M', ser_time) + strftime('%S', ser_time) / 60 ELSE 0 END) AS REAL) / SUM(CASE WHEN T1.age > 65 THEN 1 ELSE 0 END) AS elderAverageMins FROM client AS T1 INNER JOIN callcenterlogs AS T2 ON T1.client_id = T2.`rand client`