by FreeAdvice staff. In all states, the age requirement to sign a contract is 18 years of age. A child under the age of 18 is considered a minor and is unable to sign a contract unless it is for essential items. Essential items include medicines, food, and medical services. Otherwise, the minor child must have a parent or guardian consent to the contract in order for it to be legally binding. If your minor child has signed a contract for a non-essential item without your approval, the contract is not valid. In other words, you can contact the business and have the contract destroyed. Valid contracts are only so if the parent or guardian consented to the contract.