"master" is a title for young boys, but i sure haven't heard it used for, well, decades.
My grandmother would put "Master" on the birthday cards she gave me until I turned eighteen (four years ago). When I was like ten or eleven I thought it was awesome and loved getting the cards. Service/waiting staff also used it when I was younger.
Thank you for reminding me of this. Mine did the same, but I don't remember when she stopped. Even as a kid I thought it was unusual. I had totally forgotten she ever did this!! I need to go see her tomorrow and give her a hug.