I have a court order for support for my 19 yo who lives in Ny I live in Nc and the age to stop support here is 18 if out of school. I also have our 21 yo living with me and am paying for his ft college education by myself. Does the law go by where the original order was or by where I live now for aging out?

Unless you can get the order modified, NC is obligated to give full faith and credit to the order from NY.

As long as the custodial parent remains in NY (assuming that's where the order originated) then NY has jurisdiction.