What does your paperwork say? There is no age of majority in NJ and yes support can go into their twenties. The only way to get it stopped (and you have to do this) is if the child has moved out and is self sufficient,married or has joined the military. If she is going to college and living at home you are still on the hook. Make sure she applies for fifnancial aid,grants etc. before enrollment. See if you can get the support payments to the school instead of the custodial parent if not living at home. And of course,makes sure your x contributes too. Afterall she wants her daughter to be successfull right?