Just as the law requires, for ordinary contracts, that a party thereto must have reached an age sufficient to give him reasonable discretion, so, in connection with the contract of marriage, the law has required that the parties be not too immature. It must be remembered, however, that the word "infant" is not one of fixed meaning: when used with reference to ordinary contracts, and without further qualification, it usually means a person under twenty-one years of age; but in the field of criminal law the dividing line between "infancy" and "adult" responsibility is fixed at a lesser age (14 at common law). In the present connection, also, the law, recognizing that physical attributes and various social pressures may be as important as chronological experience, has commonly fixed at less than twenty-one years the age at which completely valid marriages could be contracted.
At common law, where either party was under the age of seven years a purported marriage was treated as totally without effect; between seven and fourteen years for males, and between seven and twelve years for females, the parties could contract a relationship of imperfect status, the exact nature of which will be discussed in the following sections. Where no statutory change has occurred, these ages are the limits of "infancy" in this connection in the American states.
The Law of Infants' Marriages,
9 Vanderbilt Law Review
Available at: https://scholarship.law.vanderbilt.edu/vlr/vol9/iss4/1