updated by @jayke-watson: 01/13/15 09:56:31PM
I've never forgotten the date of my birthday, but I know a few people who don't care about it so they end up not even really remembering. Maybe as people get older, it holds less excitement for them unless they're one of those super-happy people that love an excuse to celebrate something or do something. So I don't think it's very uncommon.
To me, my birthday never really been important. Well, I'll have to admit I liked the gifts and the special dinner when I was a kid, but I never felt the need to celebrate it. I actually invited friends to share this day with me only twice in my life, and really just because of social reasons or experiments. I actually don't usually talk about my birthday if not clearly asked, and never celebrate it. Well, of course, I don't forget about it cause my family members always call me on this particular day, but if not for them, I would probably simply live it like any other day of the year. In fact, I don't care about birthdays at all. I used to remember every birthday of everyone I knew, but now I usually forget people's birthday (even my mom's and husband's!). I try to remember them though, to be nice to people for who this is an important matter, but actually fail most of the time. So thanks Facebook for thinking about it for me