He will stop paying child maintenance whether the CSA are involved or not, once the children are out of full time education.... which can be any age over 16. And I think the max age limit when still in full time ed is 21.... Hope this helps
child maintainance stops on the first monday of september after they leave school. if your children are not going on to full time education (more than 12 hours per week and the course is up to and including A level). if your children go on to sixth form you will have to pay until he or she is 19 not 21 like the other submiters have told you . they are the old rules