In T318546#8336633, @Etonkovidova wrote:

Presently, a user attempting to sign up as a mentor and not having the required number of edits will see the following message on Special:EnrollAsMentor:

We should provide more specific feedback to users who try to Special:EnrollAsMentor but might not to met the qualifying criteria.

We should replace "You are not allowed to execute the action you have requested" by the reason chosen by the community. We then have two cases:

Case 1: the community defined thresholds
Communities can define a number of edits and a number of days of presence to define who can be a mentor. We should provide the feedback to the user in a form that looks like:

Users with $1 edits and $2 days of presence can signup to be mentors.

Case 2: the community relies on user roles
Communities can request to grant the access to mentorship features to a given role (autopatrolled, editor...). In this case, this reason should be given as the explanation of the error. We could reuse badaccess-groups ("The action you have requested is limited to users in one of the groups: $1").