Both at about 8 or 9. I taught them a lot before that age because of unsatisfactory schools - especially when we were living (provincial Sri Lanka) at the time I started. The older one went in an out for a bit though. Especially with maths I did a lot of fun stuff with them because I did not like what (little!) the schools were doing.

if you are familiar with the UK system they were both home educated up to GCSEs (taken at 16, end of compulsory school age here), then went to college (school for 16+) for A levels. The younger one is 18 and just finishing college - and her A level choices included maths, which is quite a turn around given she hated maths when she left school. Her older sister works in power electronics R & D.