I left school at 15 with no 'O' or 'A' levels.
When, IIRC, at the age of 22, I applied to the RAF, they required 5 'O' levels.
I could have knocked them off in a couple of months but had to wait for the exams to come around. ISTR I was considered to have maths and one or two others on the basis of post-school engineering qualifications.
Interesting that no A Levels were required!
The Airways Corporation required 'A' levels but it was clearly demonstrated by the RAF that they were not necessary for pilot training.