Lock Cells after Date has Expired

Hello all, I have several spreadsheets that users fill in on a monthly basis. These are collated into on master document used as a report. an email goes out for users to complete the spreadsheets by the end of the month. The spreadsheets are password protected and all cells are locked other than the ones which information is required to be filled in.
I would like to know how to only allow this months cells to be unlocked and as the months progress, to lock last months and unlock this months cell columns. This would stop users filling in months in advance and also highlight users that do not fill in the spreadsheets on time.
On the example, January, February and March are filled in and need to be locked as the date has expired. April allows the user to enter data and May to December also needs to be locked. Can this be achieved without VB code and just in functions?

Thanks
Paul