what is the equivalence of year 6 in the UK to the South African system?

Attendance at school in South Africa is compulsory from age 7 (grade 1) to age 15 (grade 9), although children are able to attend voluntarily from age 5 (grade 0 or reception). South African primary education begins at age 7 and ends around age 13. Secondary, or further education, is between the ages 14 and 18 (grades 8 -12). Students can choose to leave education in grade 9 or continue on to take the matriculation exam, which is necessary to gain entry into university.

Y6 in UK is the last year of Primary School. It's for students who are aged 10 before the start of the academic year (September 1st)