According to my L (and this may just be a CA thing, so consult your legal professional), child support orders can be changed until children reach the age of majority (18) or graduate high school.
W has told me in the past that with her being a federal employee, as she climbs up the salary / GS levels, at some point she will be making over 6-figures. I’m sure she will find out what that means for my requesting child support over the coming years.