Arbitrary measurements of time

There are some people who look forward to their birthdays. There are those that like to (some of them secretly) have a fuss made over them. I am not one of them.
You may hav guessed from the above that my birthday is approaching rapidly. Ever since I can remember I've never been a big fan of my own birthday. I always felt uncomfortable with the attention. Family members seemed quite upset when I would genuinely say that I wanted nothing for my birthday. I was being honest yet they didn't believe me. It's always difficult being the odd one out in your family (this is just one example of this).
On only two occassions have I had a party, my 21st and 30th. Everyone has to have a 21st. It was more of a party then a birthday. I almost got away without speeches. I thanked everyone for coming, told them to party on and that was about it. No stories. My 30th was a joint party with my friend Nick. I can't really remember too much from that one.

Why does it require a birthday (or other arbitrary date such as Christmas) for family or friends to get together? If you are close to someone then you make time to go and see them because you want to and not out of obligation. A lot of stress is caused because of this. You must of heard "But it's family and you have to go". Let's take a closer look at this. 100,000 years ago there would have been just a few families (I wonder how do you define 'family'?). If the above was adhered to, the get togethers today should be enormous. But they aren't. Why? Because those that followed the above wiped themselves out because of internal family feuds.
Having said that I should catch up with some friends who I haven't seen in a long time. I do enjoy their company and I'm ashamed to say that I've been lazy recently. So I'm off to contact them, especially Joh and Paul.