CREATE TABLE table_20492 ("Game" FLOAT, "Date" TEXT, "Opponent" TEXT, "Result" TEXT, "Bills points" FLOAT, "Opponents" FLOAT, "Bills first downs" FLOAT, "Record" TEXT)

When is the latest game the bills had 21 first downs
SELECT MIN("Game") FROM table_20492 WHERE "Bills first downs" = '21'
SELECT MIN("Game") FROM "table_20492" WHERE "Bills first downs" = '21'