Re: IB versus IGCSE
As already indicated IGCSE's are roughly the same as the old O level/ UK GCSE and are taken at about age 16.
IGCSE is a two year programme normally covering grades 9 and 10 before going on to IB in grades 11 and 12.
IB is an alternative to A levels and is generally regarded as a much more demanding course.
Best advice is to talk with the schools and ask them what they recommend for your son taking account of his school and study background to date.