In a small saucepan cook and stir orange juice and agave syrup over medium heat just until syrup is dissolved. Remove from heat. Stir in lemon juice.
Pour mixture into a 2-quart square baking dish. Stir in orange and lemon. Freeze 2 hours, stirring and scraping frozen mixture from sides of dish every 20 minutes. Cover and freeze, without stirring, 4 hours or until firm.
Let stand at room temperature 10 minutes before serving. Using a metal spoon, scrape across surface and spoon into dessert dishes. If desired, serve with additional lemon, lime, and/or orange and mint.