Child Support Termination Jurisdiction
I assume your child support order is from Colorado. If not, you will need a lawyer in the state which issued the child support order.
In Colorado, child support terminates when the child reaches the age of 19 unless the child is disabled and unable to care for themselves, the separation agreement states otherwise, or some other reason which creates the need for continuing support. Unless your X petitions the court for an extension of child support, it will terminate at age 19.