M.T.
I am not from the south, so in NY, people don't say Miss Firstname or Mister Firstname unless we are talking about a child's preschool teacher. I am 47, and most adults I knew were first name people. Relatives are never Mr or Miss or Mrs, it is a casual relationship. My mom was Grandma Audrey to the grandkids, to separate her from their other grandmas. My sister's MIL insisted that the grandkids call her Grandma Davis rather than Grandma Ellie, because she felt that it was disrespectful for them to use her first name. She didn't budge even when my sister pointed out that her grandnieces and grandnephews, same ages as her grandkids, called her Aunt Ellie.
With my own kids (HS and college aged now), I taught them to call neighbors, friends' parents, etc by Mr/Miss/Mrs Lastname and if the adult invited the kids to use their first name, that was fine.
I am fine with my kids' friends calling me by my first name.