[Typo3] Age Verification

[Frank Sutton]

I'm looking for the best and correct way to add "Age Verification" to 
the Front End User Registration extention.  I've read the tutorial on 
using Kickstarter to extend the FE User Registration, and I've 
implemented a new gender field successfully. My next step is to add age 
verification, but I'm not sure how to tie my date of birth field to a 
function that behaves like:

If (dateOfBirthField >= 13) {
    let_the_user_register
} else {
    deny_registration
} // End If

The date of birth field is of the format yyyy-mm-dd.

Any ideas or suggestions?

Thanks - Frank