Formula To Average Recent Groups

Hey all, I'm having trouble figuring out how to make a formula that will give me the average values of a recent group, and am hoping that somebody here will have a suggestion.

The formula needs to do this: Search the sheet for all the efficiency values of the five most recent dates by a specified user, calculate the average of these values, and display that number in a cell.

See the attached example. The colours are only there for clarification - they specify which cells are grouped, for example, purple indicates the five most recent dates for WILL, so all six efficiency values for those dates need to be averaged and displayed in Cell C3, in this case 145.

This will then need to be applied for the 2nd though 5th groups as well. Any thoughts?