Make hired date unchangeable to date in past

When clicking "Hired" on a candidate, the date field is changeable, we have had occasions where the person clicking "Hired" changes the date to a date in the past. If this happens, the data wont pull over to the next CSV file as the date is earlier.

The best way forward I can see, is for this date field, to either be removed totally or the user be able to change a date to one in the future or that date, but not in the past.