At what age do students normally take the IGCSE additional mathematics (0606) exams? Is 14-15 years a good age?
The Cambridge IGCSE Mathematics - Additional (0606) ‘is intended for high ability learners who have achieved, or are likely to achieve, grade A*, A or B in the Cambridge IGCSE Mathematics examination.'
Now the normal way in which British schools are structured, and by extension (for IGCSEs) this goes for many schools in Commonwealth nations, is to have final exams (A Levels, or Highers in Scotland, and nowadays sometimes the NB at age 18, two years after the (I)GCSEs are taken typically at age 16.
I go back to the time of O Levels and did my mathematics a year early - aged 15 - and got an A for that, then a year later the A/O Level along with my other O Levels. At the time it was quite common to take mathematics A/O Levels in the first year of A Level studies, but this was long before the split into A1 and A2 Levels.
Having said that, mathematics is the one school subject which could definitely be taken at a slightly younger age. Or a lot younger if you happen to be as smart as Arran Fernandez - Wikipedia who at the age of 5 got a D when he first attempted the regular GCSE and became Senior Wrangler at the age of 18 years and 0 months! The thing is, mathematics doesn't have any prerequiste subjects or even need much maturity; it just requires enjoying doing maths a lot.
In summary, the normal age will be 16 almost invariably. A student might take it as a back-up option to an S1 if they really enjoyed exams aged 17. But earlier than age 16 it is more likely they will have taken the regular IGCSE aged 14 and then the additional one aged 15 because they entered school a year early or skipped a year and are planning to complete their A-levels aged 17 rather than 18.