About finishing highschool before NS

[austincmn]

I was born in May 1997, and I am almost 15 years old now, and studying in China. I am now in the second half semester of sec 2.
Looking at China's system of schooling (school starts at September every year and not January, unlike how it is in Singapore.), I shouldn't be able to finish high school. In fact, I will be stopping at the second level of high school.
What I want to know is, do I have to go for NS strictly when I reach the age of 18, or is there a way to delay it for schooling reasons? Like for example finish high school? Is it possible to go at 19?

Also, if it is true that I must go at 18, do I have to go in May?

Added information: It's because if I stop at the second level of high school, it will really affect my graduation of high school exam or whatever it is called.

[sundaymorningstaple]

You can normally get a deferment as long as it is secondary school. But not for tertiary education post secondary.