It depends on his work experience. I'm guessing that there are quite a few posters here who are trying to get into aviation as a first serious job. If this is the case, other than your academic studies you have little to show to a potential employer so your grades do matter as it all they can judge you by.
For those who left school ten years ago or more your CV is going to need to show what you have been doing with yourself during that time and your school results will have far less importance (who cares what you were like as a child when your getting into your late twenties?).
Airflight69 should do evening school in at least GCSE English and Maths as it would be easily manageable and probably be enough to satisfy most Airlines so long as he has actually got proven, useful work experience to show for the last 10 years.