As someone who left school at 16 with visions of being a pilot (note - not "airline"), I would also backup the ideas of starting with gliding - very cheap to learn and the trick with aviation is to keep your hand in if at all possible.
I managed to be getting paid to fly at the age of 19 - but it took at a lot of hard work! The backup plan is also sound advice - while I was job hunting I still had to eat, so having skills in another area is invaluable. Don't worry so much about the degree - like people have said - if you can do well through your ATPL GS then thats proof enough you have the knowledge.
Best of luck
