What percentage of complaints are from the elderly?
elder refers to age < = 65; percentage refers to divide(sum(age < = 65) , count(client_id)) * 100%
SELECT CAST(SUM(CASE WHEN T1.age > 65 THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T1.age) FROM client AS T1 INNER JOIN events AS T2 ON T1.client_id = T2.Client_ID