Hello,
I don't think you can limit the MRP to see open orders in the past.
For the MRP, if the order reamins open, that means that it still can be delivered.
You should not have open orders in the past. What is the reason why you can not close these orders.
If the orders can not be closed for some reason, maybe you can change the Schedule line category and make the order not relevant for the MRP.
Kind Regards,
Mariano