Section 517 - Termination of child support(a) An order of current child support entered by this Court or a court of competent jurisdiction in this State shall terminate by operation of law when all minor children subject to said order have reached 18 years; provided, however, that if a child over 18 is still enrolled in high school current support shall terminate by operation of law when the child receives a high school diploma or attains the age of 19, whichever event first occurs.(b) An order of current child support entered by this Court or a court of competent jurisdiction in this State shall terminate if custody of all children who are the subject of said order is transferred to the obligated parent pursuant to an order of a court of competent jurisdiction or the written voluntary agreement of the parents.(c) Notwithstanding the above, the obligation for payment of arrears or past due support shall terminate by operation of law when all arrears or past due support have been paid.