I'm turning 24 in March, so I can relate. I actually hadn't done anything for my birthday since I was 16 until my last birthday. It was never really a big deal to me. My girlfriend threw me a surprise party, it was the nicest thing anyone had ever done for me.
It was just a few friends over, some of whom I hadn't seen in ages. We had a few drinks, did karaoke, it was a really great time.
Not sure if I'll do something this year, but it's important to celebrate every now and then.