As a newcomer to the UK but a US citizen, your best bet will probably be to return to the US for college, flight training, and flying employment unless for some reason you really prefer to stay in the UK.

Will you have right-to-work in the UK? If so you could try to do well in school and apply for the "ab-initio" programs of UK and other EU airlines (those programs take you from high school to an airliner cockpit fairly quickly). But if you can't get into one of those and have to work your way up through the aviation ranks, the US would be easier and cheaper.