Wjy do I have to enter my Birthday to join the forum?

I can't remove the question.

I looked on the Ning forum:  "No you can't remove that because NING put that there in a few release ago to get ning up to date with a few internet laws i think thats why they said they did it but your not allowed to take it out "

However, the birthday will not be displayed to anyone.

Also, I presume you can just enter Jan 1, or some year.

Al