The Osirion has been dated using surface luminescence dating techniques and the results make it highly unlikely it was built in 10500 BC:

“For the sample from the northern wall of Seti A’ the estimated age was 1070±400 BC. The archaeological age estimation is Middle Kingdom (XI to XIII Dynasties, 2030 to 1640 BC), the lower age implies possibly later re-use. For Osirion samples, RHO-138 and 139, we have to take under consideration the fact that the base of the structure was covered by sand for 1400 years. Thus a dose must be subtracted from the calculated one. Thus the age of both samples are compatible with the archaeological age attribution of XIX Dynasty (1295–1185 BC) and the Middle Kingdom (1800BC) respectively (Kemp, 1968; Brand, 2000; Mariette, 1869). (ADVANCES IN SURFACE LUMINESCENCE DATING: NEW DATA FROM SELECTED MONUMENTS I. Liritzis, A. Vafiadou, N. Zacharias, G.S. Polymeris and R.G Bednarik, 2013)

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Chris