Write SQL query to solve given problem: How old was the goaltender who scored the fewest goals while on the ice when he retired from the NHL?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT T2.lastNHL - T2.birthYear FROM GoaliesSC AS T1 INNER JOIN Master AS T2 ON T1.playerID = T2.playerID WHERE T2.lastNHL IS NOT NULL GROUP BY T2.lastNHL, T2.birthYear ORDER BY SUM(GA) LIMIT 1