Question: On or about December 8, 1989, Joseph Muller and Tina Muller, who are brother and sister, both signed a loan application with CES Credit Union. Tina was seeking the loan so that she could purchase Joseph's 1987 Buick Skylark. The loan application indicated that Joseph's birth date was February 10, 1972, and indicated that he had an automobile loan with BancOhio in the amount of $7,200 that would be paid off if the loan to Tina was approved. Once the loan application was approved, both Joseph and Tina Muller signed the loan contract. While Tina signed the contract on December 26, 1989, as the debtor, Joseph, on December 22, 1989, signed as a co-signor. At this time, Joseph was two months shy of his eighteenth birthday and the age of majority for contracting in his state was 18. The amount of the loan was $6,160.00. Joseph then transferred the Buick Skylark to his sister and his auto loan with BancOhio was paid off. Tina later defaulted on the loan, the Skylark was repossessed and sold at auction, leaving a balance of $4,915.73 owing to the credit union. In January 2003, the credit union sued Tina and Joseph seeking a judgment against them for the remaining principal and interest. Joseph defended on the ground that he was a minor when he signed the contact and that he therefore lacked capacity to contract. Is this a good argument?