Can I Have A Court Order Modified

Nine years ago my ex husband and i had a court order given to us ordering me, the ex wife to pay 153.00 a month in child support. he said he didn't want anything from me just to please not drag him into court again.i agreed. now that our children are grown (25 and 20) our son has gotten into a lot of trouble. he told me i needed to pay his dui fines.

i told him no. he is now taking me back to court for back child support.after 9 years. we obviously had an agreement. although not in writing (huge mistake on my part).i am not working at this time. can i have the order modified after not paying for 9 years. if we didn't have an agreement i would have been paying what was ordered, and would have went back to court long ago for a modification. we live in California. please help!