This half-birthday thing didn't become a thing until HS. Those days were marked with decorated lockers and balloons. A good friend of mine share birthdays/ half birthdays. Our bday greetings to each other are pretty ridiculous as we go back and c firth wishing each other happy bday/ half bday.
Pretty soon my mom's half bday is coming up and she's feeling sad about her upcoming birthday. Her mom amd grandma both died at the age she will turn later this year. I am going to send her something to commemorate her half bday. She will probably think it's silly, but that's the point because on her actual birthday I think she will be somber.
Half-birthday are really just another opportunity to celebrate someone. Do you have fun with with half-birthdays?