How many athletes over the age of 59 competed in the 2016 Summer Olympics?
over the age of 59 refers to age > 59; the 2016 Summer Olympics refer to games_name = '2016 Summer';
SELECT COUNT(T2.person_id) FROM games AS T1 INNER JOIN games_competitor AS T2 ON T1.id = T2.games_id WHERE T1.games_name = '2016 Summer' AND T2.age > 59