This is not unusual. Birthdays fell somewhat by the wayside for me a few years back, since I'm not really a party animal, and presents from family far-flung across the country don't usually arrive on the day in question. One year, I was working in an office, which of course involves writing the date approximately once a nanosecond, and spent half the day wondering why I kept wanting to write "5/28/77" instead of "5/28/99" until, sometime after lunch, the light dawned. (Hey, I never said I was bright.) And, of course, once you pass about 21, birthdays are no longer quite so milestoneish--at 25 you get to rent a car, and your insurance rates go down. Woot. At 26, my current age, I don't know if anything exciting happens, but I've learned to make my own fun--James is taking me out to the art supply store to get an easel, something I've always needed and never had room for. No more balancing art on the couch!
It turns out, amusingly enough, that my birthday coincides with a few other people on my Livejournal, and falls a day after the talented Cara Mitten's. Were I inclined to astrology, I'd say something about Geminis and creativity, but as has been pointed out, the gravitational influence of the delivering obstetrician is significantly greater than that of any distant stars, so I'll chalk it up to coincidence and statistics.