In one of the old sermons, it was said that the Sphinx was built during the age of Leo, 10,500 years ago(or so, I don't remember the exact number). It's not precise, but you could do a little math to figure out roughly when the next age will begin. IIRC, when I did it, it came out to some point later on this century, which seems to make sense given the state of the world today and knowing that there was a mass reincarnation of souls from Hell recently, and that during the hegemony of xianity we've been in the age of Pisces. We're definitely on the cusp.
Not that it matters all that much; it'll happen when it happens. The only thing to concern yourself with is making sure today that tomorrow, when it comes, will be a good thing.