I reckon it is the return of the Y2K bug! AW doesn't do the Year 2000.
Well actually they do, you have to specify a 4 digit date for the year field of your date of birth.
However, I have done a little experimentation, and it accepts any year from 1900 onwards. Hence the maximum age being 121 years at the moment. There are also other interesting validations taking place concerning being old enough to use the site, and also being old enough when you registered.