Account Registration–Age Gates: Birthdate vs Birthyear vs Age Range

Legally, because of laws both stateside and international, we are now allowed to have users under the age of 13, without obtaining parental consent. To meet this need, we need an age gate to determine whether we ask our new user to obtain parental consent or not. I have considered 3 types of UI.

1)Birthdate (month-day-year, 3 individual drop-down menus) This is typical and conventions lean toward this, however, this tends to be very personal information and offends some users why we are asking for it.

2)Birthyear (year combobox of typing or drop-down menu) Still a similar issue to point one but to a lesser degree. We also may ask some 13-year-olds to get parental permission unnecessarily because of the date that they were born on/current time of year. So accuracy goes down.

3)Age Ranges (Buckets) in a drop-down menu (ie 0-5,6-12, 13-17, 18-21, 21+) This goes a little against convention but seems a little simpler. I'm not sure it just seems a little weird to me, and it seems like I'm asking for it so I can market to the new user which turns me off.

Any thoughts on age gates? Which of these work best, or is there another solution that I could consider?

Thanks for your help!