How many years of experience do you need to have in an MOS in order to be an AIT instructor for that same MOS?

Generally, you want to have experience, but as a SSG, you probably have enough. You have to remember, AIT is about teaching the very basics to a group of people who have never seen this kinda stuff before. You'll have other instructors there to show you the ropes for the first few months. I have seen MOS-T students graduate, and then stay on as instructors. It's usually a very scripted process anyway, so your left and right limits are pretty narrow. Your experience will help to add flavor to the boring powerpoints though.