CREATE TABLE people (Age NUMBER, People_ID VARCHAR2)
CREATE TABLE gymnast (Gymnast_ID VARCHAR2)

What is the average age of all gymnasts?
SELECT AVG(T2.Age) FROM gymnast AS T1 JOIN people AS T2 ON T1.Gymnast_ID = T2.People_ID
SELECT AVG("T2"."Age") FROM "gymnast" "T1" JOIN "people" "T2" ON "T1"."Gymnast_ID" = "T2"."People_ID"