What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
You can use the DateTime tool or the Birth Date Picker widget. Here's a demo form that I've created: https://form.jotform.com/61723974874974
You can find the DateTime tool under the Quick Fields.
The second one is Birth Date Picker widget. Here's a guide on how to add a widget.
Hope this helps. Let us know if you need further assistance. Thanks!