In California, anyone below the age of 18 is considered a minor. A minor does not have legal capacity to enter a contract. If a minor enters a contract, the minor has the option to voiding the contract. However, upon reaching the age of majority, the person may take some step to affirm the contract which will make the contract valid and binding against him.
A person who is mentally impaired and incapable of understanding the nature of a contract when she enters into the contract, cannot be forced to perform under such a contract. However, if this person should recover from her mental deficiency, then she can affirm the contract and the contract becomes enforceable against her.
A person who is intoxicted to the point that he may not understand the nature and significance of his promise, can choose to void any such contract entered into. Intoxication may be caused by consumption of alcohol, prescription drugs or even illicit drugs. However, upon recovery from the intoxicated states, this person may affirm the contract at which point the contract becomes valid and binding against him.