What age group has a time of 6:37.73 at the 200m breaststroke?
CREATE TABLE "master_world_records" (
  "pool" text,
  "age_group" text,
  "time" text,
  "event" text,
  "date" text
);
SELECT "age_group" FROM "master_world_records" WHERE "event"='200m breaststroke' AND "time"='6:37.73';