IF he has the legal capacity to enter into a contract the other party may enforce it. If he did not have the legal capacity to enter a contract then the other party should be apprised of the situation. You should consult with an attorney in your area ASAP.
Legal capacity:
- Capacity relates to soundness of mind and to an intelligent understanding and perception of one's actions. It is the power either to create or to enter into a legal relation under the same conditions or circumstances as a person of sound mind or normal intelligence would have the power to create or to enter.
- A person of normal intelligence and sound mind has the capacity to dispose of his or her property by will as he or she sees fit.
- An individual under duress lacks the capacity to contract.
