If by "back pay" you mean, support that was ordered and not paid - yes.
No.
no not at the age of 20 years of the child. It may be of 25 years of the child
arrears - yes; current (ongoing) support - yes, if the child is still a minor/dependent; retroactive support - maybe, it depends on several factors
No.No.No.No.
You cannot collect child support from 40 years ago. The statute of limitation has long passed.In Illinois at least, there is no statute of limitations on unpaid child support relating to an existing order.
If she's kept the claim current.
Yes, up to 18 years retroactive.
Yes. You are not paying for the mother, you are paying for the child. If that were the case, children living on college campuses whose custodial parent has an extended modification to child support granted or are attending boarding school would not be able to collect support. If the child is living elsewhere without permission of the court and/or if that move would constitute legal emancipation as outlined by your state's laws, you do have the right to file for modification of child support based on the same.
Of course because they are still his children and he is responsible for supporting them.
You usually pay until the child is 18 but the laws vary between states and countries and it also depends on what the child support agreement says. How long you pay child support does not change whether you still have your parental rights or not.
Can the state of Texas collect on a court order for arrearage for child support from the state of Arkansas even though the state of Arkansas has a statual of limitation which is three years and five years if the child is eighteen but the mother didn't open a child support case with the state of Texas fourteen years later
If she is still nursing a child.