Write SQL query to solve given problem: In the calls from the mountain division, how many are from teenage clients?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT COUNT(T1.age) FROM client AS T1 INNER JOIN district AS T2 ON T1.district_id = T2.district_id WHERE T1.age BETWEEN 12 AND 20 AND T2.division = 'Mountain'