Get the Average from Date from Checkboxes

I am trying to put together a sheet for tracking student scores based on criteria. I have made checkboxes (that work!) that when checked, give the averages of criteria. 

My next step is to make a formula that will gather all same criteria as the row in the checkbox and average them from that point. 

I have the formula that will get the minimum date and the matching criteria to that date. From here I need to figure out how to get the average of all criteria in a date greater than the date from the box that is checked.