I can’t answer on the alimony, that issue would depend on several things including what the orgininal agreement states.
As far as the child support, it should be age 18 or until graduation from high school. As long as the child is making an effort to graduate. This covers those children who turn 18 before graduating, or who are still 17 after graduting. If the child is not going to graduate, planning to quit school or fails then the parent can claim that the child is not making the effort to graduate and can have the courts allow him to stop paying child support at the age of 18. But this does take going to court. If the child turns 18 and/or gradutates high school then the child support does not legally have to continue, unless there is something in the agreement that stated that support would continue…