forms - Are users reluctant to give their complete date of birth?

I am required to ask users their DoB, but only for verification purposes, to make sure the user is over 18 years old. This info is one of the 6 things I ask in a Sign Up form to participate in a beta site, so it's a small form.

Because I am slightly reluctant to give a precise date myself, I wonder how necessary the info really is. I would be more comfortable myself picking a month and a year, but no so much a day (security reasons.) However I haven't seen this anywhere, and it feels quite strange.

In short:

Would it make sense / feel okay to ask for MM/YY only instead of DD/MM/YY?

Answer

This doesn't really answer the question whether users are reluctant to give out their date of birth in general. I know I am. I usually give the wrong day.

Instead of asking for a complete date of birth, you could just ask if the user is over 18. If they are willing to lie about their complete date of birth, they will lie about being over 18. In that case it is their risk, not yours. This isn't for a governmental health care application, right?

You also get rid of two fields in the form.

And even better, if you incorporate the verification into the submit button, there are even fewer fields to clutter up the form: "I'm over 18 and want to use your site."