Go for it
Hi there, i´m almost 40 too, and i´m finishing ATPL-H ground school in order to do a conversion from ICAO to JAA, so i had to do all the theory again (JAA), so that i can fly in Europe.
Check with bristol Ground School, where you can do you theory course, from what i know you will have no problem with the GCSE´s, and they are very professional.
Go for it mate, it´s a long way, but it pays in the end
Best of luck