I get a chuckle over this every time it happens. Something in one of the many synch tools I use does some sort of conversion of birth dates, and I end up with alerts on my Mac that tell me somebody is having a really great birthday:
I also see the opposite where I’ll get a reminder that today is somebody’s second or third birthday.
In the case of the ones where they show up younger, it’s usually because wherever I got their birthdate from originally, they didn’t put in the year. So that usually ends up being the year that the contact was entered into my address book.
But in the case of the incredibly old dates, my address book typically has an 1800’s date, so my guess is it’s some system breaking on a date overrun. I’ve also noticed that sometimes these contacts have two birth dates in my address book (again, some symptom of a synch problem), so for instance Reinald has both a birthday in the 1800’s and one a littler more reasonable than that.