The statistical age norm per grade is the grade number plus 6.
Example:
Grade 1 + 6 = age 7
Grade 9 + 6 = age 15
Grade 12 + 6 = age 18
Also note a reference in Notice No. 2432 of 1998, GG 19377, where Section 29 states: A learner who is 16 years of ages or older and who has never attended school and who is seeking admission for the first time or did not make sufficient progress with his or her peer group, must be advised to enrol at an Adult Basic Education and Training (ABET) Centre.