Yes you have to pay all support .
Yes.
no
no it goes to the mother.
For what is he wasn't required to pay?
Petition the court for a modification. If the back support was for any state aid the mother was on, then it can't be forgiven. If it isn't for that, then the mother can write a letter saying she forgives the back support owed to her.
Yes, he is still the father.
Federal law limits it to 18 years old
In theory, yes. However, the court will not likely order support prior to the time that the father knew about the child. The court should also take into consideration any voluntary support the father gave.
no, you would have to go through the legal processes.
If you were overpaid, yes.
yes
It is very doubtful. Thirty years is well past the statute of limitations for debts.