My child almost 17 years old. I would like to ask you the following questions:
How long I have to pay child support in NY state? When I am able to stop?

Usually this is defined in your child support order. In NY state the law says up to 21. It could be even older if the child is a full time student.

In no state is it under 18. In many it is all the way to 21 especially if a full time student. You should be able to look at your order to find out when yours stops.