Hello @rbk69!
As I understand, you want to add a ‘Date’ field, preferably on the ‘Checkout’ page to collect the birth day information of your users. Is that correct?
If yes, then we have an extension named WooCommerce Checkout Add-Ons that allows adding custom fields to the Checkout page.
However, with this plugin, there is no option to add a ‘Date’ field; but, you can add a text field and make it required. Users will have to type in their birth date manually into it.
If this doesn’t solve your purpose, you might be able to find a third-party plugin that allows adding the date field on the checkout page.
Let us know if you have questions or if you are referring to something else.
Best!
