The contract age of majority is currently age 18. Contracts entered into by minors under this age are generally voidable at the minor’s option. This contract doctrine of capacity is based on the policy of protecting minors from their own poor financial decisions and lack of adultlike judgment. Conversely, the age of 18 is currently set as the arbitrary age at which one will be bound to her contract, since this is the current benchmark for becoming an “adult.” However, this article questions the accuracy of age 18 for this benchmark. Until comparatively recently, the age of contract majority had been 21 for centuries. The age was reduced to 18 in the aftermath of protest over the military draft of 18-year-olds during the Vietnam War during the 1960s and 1970s, and the enactment of the Twenty-Sixth Amendment which lowered the voting age from 21 to 18. However, the appropriate age for the military draft bears little to no relation to the appropriate age for voting, or contracting. Moreover, other evidence points in the direction of age 21 as a more appropriate age of majority. First, scientific evidence of brain development has advanced to the point that we now know the brain does not stop developing until well into the 20s, which means the powers of cognition and decision-making are not fully developed until then. Second, sociological evidence suggests that most people do not perceive the full attributes of adulthood as having been reached until at least 21, if not older. Third, other areas of the law have experiences in coming back to age 21 as an appropriate marker of adulthood --- these include the age for purchasing alcohol, the age for obtaining a credit card, and soon (it appears) the age for purchasing cigarettes. This confluence of evidence suggests that the contract age of majority was always appropriately set at age 21, and a return to that age of capacity for contracts will correct a historical misstep in the law.