Just a bit older?
A few thousand years?
Just before the flood?
tens of thousands of years earlier?
or WAAAAAAAY older?
If the casing stones were an integral part of the system and therefore can be assumed to cover all those pyramids at some point, then you can assume that the inner core of stones havne't been exposed to the elements to display their true age so its not ridiculous to push the outer limits of their age quite far. Just interested to hear how far others push them back.