bbPress roles are not wordpress roles. So it doesn’t show here.
If you need custom role you can use user role editor plugin. Do not forget to set those as wordpress role.
This should not be that complicated. But will require many code.
Thank you for your nice suggestion. I have added it to our to-do list. May be in future we will add this as core feature of this plugin.
If you need it now you can contact me using https://www.shamimsplugins.com/hire/
You can achieve this my running a cron job and query messages using FEP_Message_Query which is created more than x years ago. Then archive those messages.