The Clear Old function in School Announcements Easy was designed to remove old items from the Form Submissions sheet based on date. In April or May of 2018 this function stopped working. An update on the SAE Add-on was published in August of 2018 that temporarily solved this problem. However, the update was related to other issues and did not address the problem in Clear Old.
Until this issue is solved, Old items can be removed manually. This process can be sped up by using the Sort Range command in the Data menu of Google Sheets.
The next update of SAE will include conditional formatting to color code dates. This should help deleting old items manually until this issue is fixed.