Age change is a legal act, recognized in practically all legal systems, which allows a person to adopt an age different from their age at birth. The procedures and ease of an age change depend on the jurisdiction. In general, common law jurisdictions have rather loose limitations on age change, while civil law jurisdictions are quite restrictive.

State laws can regulate age changes in the United States. Several specific federal court rulings have set precedents regarding both court-decreed age changes and common-law age changes (changing your age “at will”).

Usually a person can adopt any age desired for any reason. Most states allow one to legally change one’s age by usage with no paperwork, but a court order may be required for many institutions to officially accept the change. Although the States (except part of Louisiana) follow the common law, there are differences in acceptable requirements; usually a court order is the most efficient way to change one’s age (except on birthdays, which have become a universally accepted reason for age change). It is necessary to plead that the age change is not for a fraudulent or other illegal purpose (such as evading a spouse or lien, or for defaming someone).

The applicant may be required to give a somewhat reasonable explanation for wanting to change his age. A fee is generally payable, and the applicant may be required to post legal notices in newspapers to announce the age change. Generally the judge has limited discretion to grant or deny a change of age, usually only if the age change is for “frivolous” or “immoral” purposes, such as changing one’s age to 13, 18, 21, or 39.