Calculate the average age of clients from the Midwest region.
average age = AVG(age);
SELECT CAST(SUM(T1.age) AS REAL) / COUNT(T3.Region) AS average FROM client AS T1 INNER JOIN district AS T2 ON T1.district_id = T2.district_id INNER JOIN state AS T3 ON T2.state_abbrev = T3.StateCode WHERE T3.Region = 'Midwest'