I taught T2 in a training college with four “grades.” My students were 16 to 32. The reason some were so old was they were required to take two years off from school when they had a baby. The 32 year old had 4 children. 16 was the right age for the grade. Students did 6 years primary and 4 years middle though if a student was accepted to secondary school he/she only spent 2 years at middle.