what is the sport when the age group is 21 or younger and the competition name is world youth netball championships?
CREATE TABLE "women" (
  "sport" text,
  "competition_name" text,
  "competing_entities" text,
  "age_groups" text,
  "held_every" text
);
SELECT "sport" FROM "women" WHERE "age_groups"='21 or younger' AND "competition_name"='world youth netball championships';