Thanks for reaching out to Jotform Support. Our Spanish Support agents are busy helping other Jotform users right now, so I'll try to help you in English using Google Translate, but you can reply in whichever language you feel comfortable using. Or, if you'd rather have support in Spanish, let us know and we can have them do that. But, it might take a while until they're available again.
Now, coming back to your question, you can use the Date Picker and a Number element and create a condition to calculate a person's age based on their date of birth. Let me show you how:
In Form Builder, click on Add Element + on the left side of the page.
Under the Basic tab, find and add 2 Date Picker and 1 Number elements into your form.
Click on the Gear icon right next to the second Date Picker element to open its Properties.
Go to Options tab and set the Default Date to Current.
Then, click on Settings in the orange navigation bar at the top of the page.
Select Conditions in the menu on the left side of the page and choose Update/Calculate Field.
Set up the conditions like shown below and click on Save.