I would suggest, that all this.. weathering stuff...is totally irrelevant to either the age of this sublime entity..., or to its identity.
It is of no consequence whether unseasonal torrential rains poured down upon the north face, the east face..., whatever......,of this sublime beasts enclosure. There is something of much more importance at stake here.
The concept, that this entity was supposed to represent a Lion..., is amusing..., but then; WHY doesn't it look like a Lion. Why does it look like the most noble, the most awesome, aware..., the most eternal human presence that has ever been given form in rock or clay?
This is the great mystery of the Sphinx; it defies analysis by shoddy, plodding, myopic academics.., because it is beyond the perception of the mediocre; it is really only accessible to those who can accept the concept of eternity without predudice or preconception.
It will live on when most of us are..., how shall we say- less than dust.