Unfortunately these days just being good at something isnt enough. You have to have a certain amount of qualifications before you can even get on the course esp in maths.
Sadly .gone are the days where one could join as tea boy etc and work their way up and learn a trade.
You probably have all the required GCSE'S etc and should have no problem, but my son was keen to do plumbing and didnt have enough , as hes got moderate learning difficulties so he couldnt get on any plumbing courses.
Give a man a fish and he will eat for a day. Teach a man to fish and he will eat for a lifetime.