mummytime, I deal every year with dozens of parents and pupils who have this misconception, they are not only out on their ear, to put in bluntly, but often apparently gobsmacked to that this is the case.
I can't think why, it is perfectly straightforward. You have three years free sixthform education, so can repeat GCSEs, or take a one year course, before taking a two year course, if necessary.
That is your lot. Full stop. Then you are out.
It is nothing to do with the school, it is government funding. Unless the school funds a student interdependently. This can happen, and does happen, which might be why the wrong message is often picked up. This is dependant on the school making a saving elsewhere, having no other applicant for that place, having no other student using the "guest funding" and, most important of all, having an "moral obligation" to do so. For example, a student with cancer got it in my tutorgroup last year, and a couple of years before that, a student who had been imprisoned, then later found not guilty.
The very rare occasions when a school chooses to do this should not be held up as examples of what is available to everyone. Staying behind a year early in your education is not a reason.
It is all very well saying it is a long way off and you don't need to think about that yet, but when are you going to think about it OP? Your child will need to skip a year at some stage, if they repeat a year now.