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.
Thanks for contacting us.
Our form builder does not have such functionality. However, I think there's a workaround that we could do using conditional logic. Please take a look in this form: http://form.jotform.co/form/33395241468863
I was able to accomplish that by adding two Age fields, one is set as required and the other one is not.
Then, I created this condition:
If Will you attend to the event? Is equal to Yes Show Age (required) and Hide Age.
I used the show/hide method to build the condition:
I hope this helps. Inform us if you need further assitance.