At a young age, I observed a few things:
At some point, I stopped telling people my birthday, and I removed the date from every account of mine online. This confirmed my first observation listed above, as almost nobody wished me a happy birthday without Facebook reminding them. As the years went on, fewer and fewer people remembered my birthday, and even my own mother has forgotten to wish me a happy birthday several times. I have plenty of friends who used to know my birthday, but have forgotten the exact date because there’s been nothing to remind them and they never wrote it down anywhere.
To me, this is a clear indication that birthdays aren’t very important. To an extent, I understand people being happy that they’ve made it another year, but I find no reason to burden people with the knowledge of my birthday. I don’t want people to feel obligated to write it down or try to remember it. Likewise, I don’t want to indebt myself with the obligation of wishing everyone else happy birthday. If I remember, then I remember, but if I don’t, then I don’t want anyone to be upset with me.
If you are a close friend of mine, chances are that I’ll try to organize a get-together around the time of my birthday. However, you should only attend if you want to. I have skipped plenty of my friends' birthday parties because I didn’t think I’d enjoy them (e.g. at bars, clubs, etc.).