Education
I see from your basic details that FIFE is your location.
So looking at the Scottish education system ~ good passes at Standard Grade which have now been replaced by National 5s. Maths & English are critical, together with physics.
SIN, COS & TAN is as difficult are it gets.
Success with good grades at HIGHERS will demonstrate the necessary learning curve. Again Maths & Physics would be beneficial, although not critical.
Advanced Highers even better.
As for the airlines, BA specify minimum school grades for their sponsor route. A degree is not necessary, but probably beneficial both demonstrating sufficient grey matter, and of course 3/4 years more maturity.
The modular route ~ some airlines require a minimum overall average mark in the exams. Some say 85%, others 90%. A high mark in Navigation shows that your brain is wired up well for flying.
Being a team player is critical. An accomplished sportsman where hand to eye coordination is demonstrated.
Lots to learn ~ high volume, reasonably low grade material. Just nibble away at it, on a daily basis.