Steps to reproduce:

1. As a user with rights to edit Special:ManageMentors, click to edit some mentor's settings.
2. Click the checkbox Is away? and enter a date that is in the past.

3. Click Submit - no warning will be given on incorrectly entered date. The save will silently fail.

Expected behavior

• a user should be warned the date is incorrect or it should not be possible to select days in the past. The issue is present only on Special:ManageMentors. Mentors while setting their Away status can enter only number of days:

Note: Since there is no record of changing Away setting in the history on MediaWiki:GrowthMentors.json, it could be confusing for users to figure out what was wrong with saving updated Away status.