ACF Date Picker field convert to Age and populate field

I have a Date Picker field in the backend which is used for people to select their Date of Birth, what I need is once the field has been filled out, is for another field to dynamically populate itself with the workings out of 'Current date - Selected date'.

The problem I'm having is with creating this field that will populate itself. Is it even possible using ACF? I've been through the docs of ACF and tried out their update_field() function but to no avail.

Thanks

via Chebli Mohamed