Write SQL query to solve given problem: How many years were there after Don Waddell retired and became a coach in NHL?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT MAX(T2.year) - MIN(T2.year) FROM Master AS T1 INNER JOIN Coaches AS T2 ON T1.coachID = T2.coachID WHERE T1.firstName = 'Don' AND T1.lastName = 'Waddell'