I am not atall sure why DC take exams early.
I have read of a couple in the local paper ( in August) who it seems had around 8 GCSE A* One was 10 ( still in primary) and had taken maths physics and something or other else and the older brother ( 11) had astronomy, maths physics Latin chemistry and French or some other MFL.
They were both embarking on English , history, geography and something or other else this year it seems as well as AS maths and physics. So before they are even 14, let alone 16, they will have done the NC GCSE curriculum to death. I ask what for because in reality it is very difficult to get most universities to take a DC early (even a 16 year old. I had one of those last year and the universities wouldnt take her without a chaparone
But maybe better that than boredom. I dont know. For such able children though I think maths challenge is a waste of time.
If it were my own DS I would have to consider it to be honest. Do I let him get bored silly or do I put him in for the challenge. As someone who was forced to wait ( and I had covered the work when I was 13), I recall being very frustrated by having to make pace with my peers and although I did very well, I am sure I could have done better with real support rather than being held back.
The think is too clever by half DC's (such as me and my DS oe even my DW, but as a musician she was allowed to move at her own pace) are out of kilter anyway.