How can I calculate the age based on Date of Birth entered?

how can i calculate an age based upon a DOB entered

Although we don't have an innate feature like this, you can still achieve the same goal by using the Form Calculation Widget.

Related guide: How-to-Add-a-Widget-to-your-Form 

For this, you'd need to use the floor() function to get the base result in case there are decimal places since age is always a whole number.

Your general formula would be:

floor ((TODAY - DOB) / 365.25)

1. Add a Date Picker field where the respondent can enter his DOB

2. Add a 2nd Date Picker that will be hidden and will always show Today's date

3. Add the Form Calculation widget

4. Click the ... 3-dotted menu to add the floor() function

5. Then complete the formula as shown above

Result: https://www.jotform.com/70964408638971