Form default value setting for json

I have a form with user name, email, and user detail information like DOB, address. In the database, I have aggrate the DOB and address into a json format, but on the page, it stays in parallel with user names, emails.

So on edit page, what's the best way to render default value for DOB and address through Form, of course I could read the data and using $FORM->setDefault(), but is there other ways to do it in Volt?