How long would a BA in elementary education take if you already have a AA in Arts?

It depends on what your AA is in. In other words, if your AA is in - lets say - journalism then not as many credits would be able to be placed into an elementary bachelors degree than if your AA was in elementary education or even straight liberal arts. It will depend on the receiving institution, their transfer credit policy, and the number of free elective areas with their elementary education program of study. In addition, it will also depend on your specialty within elementary eduction (science, English, math, history etc.). Certainly it will not take as long as the entire program of study, however you should - as best you can- put the time element aside. The most important thing is achieving your overall career goals and objectives. If teaching is your passion, then concentrate on being the best teacher you can. The academic counselors and program faculty should be able to guide you appropriately. Much of your AA should be transferable to your BA in elementary education.