In British Colonial America legal age, also referred to as the age of majority, was 21 years of age for a male and 18 years of age or upon marriage for a female.
For specific colonies and specific time periods, laws and statutes should be consulted to ascertain the actions that could be performed upon reaching the age of majority. However in general, a person of legal age could patent land, devise land in a will, sell or purchase land, witness a will, become a guardian, be a plaintiff or defendant in a lawsuit, or serve on a jury.
Minors of a certain age could choose their guardian, make a will, and devise personal property and sometimes real property.
Understanding the actions which can and can not be performed until the age of majority is reached aids genealogy research in many ways. It can eliminate or prove an identity when individuals share the same name. It can determine where real property has descended. It can determine when real property has descended. It can help estimate a birth date when there is no birth record. It can help estimate a marriage date when there is no marriage record.