Alive By Date

If an ancestor marries on 1 December 1901 and it is indicated that he was “of legal age,” on that date, then (if 21 is the legal age to marry) he was alive by 1 December 1880. Marrying, buying property, naturalizing, and other “legal acts” require a person to be of age even if their age is not stated in the document.

Of course people will lie about their age, but that’s a separate tip.