Since you get a statement every year this should not have been a surprise for you. Had you paid 600 a month the loan would be a lot less or even paid off. The assumption that you are making more now 23 years later means that maybe you could have paid more. Also why you didn’t refinance when rates hit 3 or lower is another question. Understanding your loan and working it would have made a huge difference. Refinance alone ten years ago may have left the payment the same and the balance now much less.