Hi and sorry for late reply,
I'm not sure to understand well...anyway a simple solution is this:
- Override profile page: copy file from /components/com_jsn/views/profile/tmpl/default.php to /templates/your-theme-folder/html/com_jsn/profile/default.php
- In the new file, after line 24 add a code that calculate age and store the information in a hidden field:

$from = new DateTime($this->user->dob);

$to   = new DateTime('today');

$this->user->age=$from->diff($to)->y;

$this->user->save();

NOTE: I assume "dob" is the alias of Date of Birth field and "age" is the alias of the hidden field

Now everytime the user show the profile then the hidden field that contain a age will be update, so you can assign conditions at the hidden field to show/hide other fields

Hi-
Thanks for the reply. No worries about the delay. This whole project has been on delay due to all the COVID19 weirdness. I am now finally getting back to this. If I am understanding this correctly, what you have given me is something that would happen when the user pulled up their profile after initial registration, not at the time of registration. I need the age field to be updated on change of the dob field BEFORE the initial save. It cannot wait until after the user has been created.

Maybe I will just resort to the awkwardness of the user filling out dob and age at the time of initial registration, and then using your idea after initial registration.

Thanks again.