What is the percentage of champions at the age of over 30?
DIVIDE(COUNT(competitor_id where age > 30), COUNT(competitor_id))as percentage where medal_id = 1;
SELECT CAST(COUNT(CASE WHEN T2.age > 30 THEN 1 END) AS REAL) * 100 / COUNT(T2.person_id) FROM competitor_event AS T1 INNER JOIN games_competitor AS T2 ON T1.competitor_id = T2.id WHERE T1.medal_id = 1