What was suggested to us by F1 and works great is to input the year 1900 for anyone that you do not have the birth year for. It does mean that you must run any reports that include age with the knowledge that some people will show up as 109 years old, but in general this works great for those who do not want to give their age.
We run P1100E which gives us birthdays by status in the date range that we select (in our case by month). Another good one is M1000 which gives birthdays by attendance in a given date range.
Hope this helps!
Lauren Wood
Church of the Living God
Manchester, CT