CREATE TABLE table_63668 ("School" TEXT, "City" TEXT, "Team Name" TEXT, "Enrollment 08-09" FLOAT, "IHSAA Class" TEXT, "IHSAA Class Football" TEXT, "County" TEXT, "Year Joined  ( Or Joining ) " FLOAT, "Previous Conference" TEXT)

What year did the team from City of Aurora join?
SELECT AVG("Year Joined (Or Joining)") FROM table_63668 WHERE "City" = 'aurora'
SELECT AVG("Year Joined (Or Joining)") FROM "table_63668" WHERE "City" = 'aurora'