I have found that most non-jws don't make much hoodoo about adult birthdays (maybe because getting older is not something to celebrate, although it beats the alternative). Based on my never-jw friends attitude, few do it annually. They might celebrate 40, 50, 60, 70, etc., for having made it to that milestone. Or celebrate children's birthdays.
But, if you are a jw and don't celebrate as well, it can be a bone of contention between jws and non-jw relatives. But that's some families. Many things to fight about.