I'm not sure if this in the right section :confused: I am seventeen years old (eighteen in November) and my family have a visa to move to the U.S.A in August, (I live in England) I have completed AS Levels. Where on earth would I be placed in terms of education? Would I be in my senior year of high school along with those a year younger than me! Please help

You may have two options, but you would need to inquire at the specific high school you might attend and the college (not 6th form college but either a community college... less expensive, often smaller classes, easier to get into for most, or university... "college" can be used to refer to either one) that you could likely attend in whatever area you will be living in. There is not an exact match coming or going on either side of the pond. For example, my daughter was put into 6th form at 16 when she did a term of study in England because it wouldn't have made sense to have her in year 11 with everyone getting ready for the GCSEs.
If you go the high school route, you won't really stand out in respect to age as many seniors will turn 18 part way through the year, but you may want to inquire about taking AP (advanced placement) courses. Going to the high school may be an easier adjustment coming over, and would allow you to get a taste of all the activities American high schools have. It would be more structured than 6th form was so it could feel like a step back in that regard. Pro... there is no tuition.
If you decide on the college route, having your GCSEs and A levels done would likely be your ticket in. You would probably take placement tests to verify your skills in English and Math. College/University will obviously give you some more freedom of choosing classes and the days/times you want to take them, as well as start you on your way if you were planning to study for a specific degree. You would be paying to attend however.
If there is anything specific I may be able to help you with, feel free to send me a message... happy to help if I can.