That area is NOW the Tropics and Sub Tropics, but the last time it had rain to any large degree was 10,500 BC.
So todays scientist say the old ones were wrong!
Plus it was covered with sand till the late 1800's.
In order for the Sphinx to have the water erosion that it does, it would have been subjected to many thousands of years of rainfall. If that was true, and historical climatology suggests that the last significant rainfall was 10k years ago, then it is reasonable to date the sphinx as even older than 10, 500 B.C.. There are some that say it is more on the order of 54,000 years old, and not 4500 BC as modern egyptologists propose.