How to calculate the difference between a date attribute registered in a DateTimeField and the current date?

How to calculate the difference between a date attribute registered in a DateTimeField and the current date?

Hi
I am creating a form to collect the data of a group of patients (id, name, dateBirth, sex, age). I would like to be able to calculate the age from the date of birth so that I do not have to request it in the form.
Could you help me?