Even better, just make the user input dates using a calendar date picker widget instead of a text field. This gives you full control of the input.

I always find that a little annoying: it takes way too many clicks (esp. for a birth year) and then you've got to find the day of the week.

I'd hate it less if typing updated the widget.

I've had to click back once per year old I am sometimes. I'd rather just type my birthday.