Maximum Character Length Add-on can limit the maximum number of characters a user can type in a field added and managed by Profile Builder.
This addon is included in the main Profile Builder plugin. To activate the Maximum Character Length Add-on navigate to the Add-ons page, locate it under the Free Add-ons sections and click Activate.
After you activate the add-on a new option will be available for your fields in Profile Builder -> Form Fields.
All you need to do is set the desired value. You can also modify this value when editing one of these fields.