Point of clarification - this is not a moral issue. Are creditors making a moral choice when they approve people for credit they should not at 18% interest rate?
This is a business decision. What will you gain from paying a 20 year old debt if it cannot be legally enforced or reported on your credit report? The law is designed to protect you from exactly the issue you are dealing with. The previous post is right - your debt has probably been sold numerous times for pennies. If they get $5 from you they have profited (which is why they do it). They may also try to con you into signing a reaffirmation agreement (a new contract to pay).
I try never to tell people what they "should" or "should not" do because I do not stand in their shoes - but this one seems easy.
Other than feeling better because a high school kid called you and said you should pay it, is there any particular reason you are considering paying?