When I was young I would get birthday cards in the mail addressed to me as Master XXXX XXXXX
And it was from people who knew my dad and worked with him in NYC.
Apparently little people like me when addressing an envelope were addressed as Master.
Current usage in the United States Nancy Tuckerman, in the Amy Vanderbilt Complete Book of Etiquette, writes that in the United States, unlike the UK, a boy can be addressed as Master only until age 12, then is addressed only by his name with no title until he turns 18, when he takes the title of Mr.,[4]:?662? although it is not improper to use Mr. if he is slightly younger.
Robert Hickey, deputy director of the Protocol School of Washington, states that "use of Master [as] an honorific when addressing boys is considered old fashioned outside of conservative circles."[5]