How do I edit the birthday calendar?

You can't edit it directly.
It is a new feature in iOS4 and it gets its information from the Birthday fields in your Contacts.

Works the same way as the Outlook calendar but better, because it directly reflects your Contacts list. If you remove a contact or a birthday entry, the calendar instantly reflects that.

There is currently a known issue with people born around 1932 where their birthday doesn't show

That's another bug I forgot to mention.
Edit your contact and put the date in again. It should then reflect correctly in the calendar.

Good. Please mark posts as Solved or Helpful if possible as it keeps the forum working properly