Unless displaced by the particular provisions of Titles 1 through 10 of this article, the principles of law and equity, including the law merchant and the law relative to capacity to contract, principal and agent, estoppel, fraud, misrepresentation, duress, coercion, mistake, bankruptcy, or other validating or invalidating cause shall supplement its provisions, except that

            (a)      the age of majority as it pertains to the capacity to contract is eighteen years of age; and

            (b)      no person who has attained the age of eighteen years shall be considered to be without capacity by reason of age.