Mattie

In 2018, 83 is the most common age for an American (U.S.) Mattie* who is registered female with the Social Security Administration. It is the 773rd most common female first name for living U.S. citizens.

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*as a first name, not a nickname.

This appears to have been a common nickname for Margaret (at least in the US) in the 18th and 19th centuries, because I come across it a lot while doing genealogy research.

The name Mattie was given to 265 girls born in the US in 2015.