Jesus,
When I started the ATPL course, I had been an industrial plumbing and heating engineer for 16 years and had left school with no academic qualifications. But after alot of study I am the proud owner of an FATPL MEP/CPL/IR. So it is possible to get to where you want to be with out having loads and loads of qualifications.....I'm proof!!, but as you are only young I would suggest not doing it my way as I found the course very challenging
, if you study hard now then studying later won't be a problem and it will save alot of late nights!!
as I know other people reading this would agree!!
As for which subjects to study at school, study the subjects
you want to learn, but as easy pilot say's maths and physics are good one's to have ( even though I don't!!).
Hope this is of some help,
M.