A mentally impaired person may ratify a contract only after he or she has regained capacity. If a person was mentally impaired at the time of entering into the contract, the contract may be voidable. This means that the person has the option to ratify or void the contract once they regain capacity. However, it is important to note that the rules regarding mentally impaired persons and contracts may vary by jurisdiction, and the specific circumstances of the case may also be relevant. It is always advisable to consult with a legal professional in such cases.