The general rule is this: minors (or more legalistically “infants”) are in most states persons younger than seventeen years old; they can avoid their contracts, up to and within a reasonable time after reaching majority, subject to some exceptions and limitations. The rationale here is that infants do not stand on an equal footing with adults, and it is unfair to require them to abide by contracts made when they have immature judgment.
The words minor and infant are mostly synonymous, but not exactly, necessarily. In a state where the legal age to drink alcohol is twenty-one, a twenty-year-old would be a minor, but not an infant, because infancy is under eighteen. A seventeen-year-old may avoid contracts (usually), but an eighteen-year-old, while legally bound to his contracts, cannot legally drink alcohol. Strictly speaking, the better term for one who may avoid his contracts is infant, even though, of course, in normal speaking we think of an infant as a baby.
The age of majority (when a person is no longer an infant or a minor) was lowered in all states except Mississippi during the 1970s (to correspond to the Twenty-Sixth Amendment, ratified in 1971, guaranteeing the right to vote at eighteen) from twenty-one to either eighteen or nineteen. Legal rights for those under twenty-one remain ambiguous, however. Although eighteen-year-olds may assent to binding contracts, not all creditors and landlords believe it, and they may require parents to cosign. For those under twenty-one, there are also legal impediments to holding certain kinds of jobs, signing certain kinds of contracts, marrying, leaving home, and drinking alcohol. There is as yet no uniform set of rules.
The exact day on which the disability of minority vanishes also varies. The old common-law rule put it on the day before the twenty-first birthday. Many states have changed this rule so that majority commences on the day of the eighteenth birthday.
An infant’s contract is voidable, not void. An infant wishing to avoid the contract need do nothing positive to disaffirm. The defense of infancy to a lawsuit is sufficient; although the adult cannot enforce the contract, the infant can (which is why it is said to be voidable, not void).