Ability to set branch retention for deletion

Currently, in a repository, there are users or teams have a number of branches left unused after merged to "master" branch.
The hard part is, manually deleting those "unused" branches.

Feature Request:

It would be best if we can have a feature that will allow users to set retention period for deleting those unused branches.

For example: Delete all branches which are more than 3 months old.

Note: At any cost, it shouldn't be deleted without any prior confirmation from the respective owners.