Is there any way of displaying a person's age based on the birth date they submit using a date/time field?

Please see the following form template that can help you with calculating age based on date of birth.

https://www.jotform.com/form-templates/calculate-age

You may use the form calculation widget to calculate the age by years using the difference of dates.

1. The following fields are added to the form to calculate the age. The Today field is set to be displayed the default date from the field properties.

2. The Age-days, Age-Years are the calculation widgets with the formula as shown below:

Please give it a try and let us know if you need any further assistance. We will be happy to assist you further.