Yes, we're in the Piscean Age. The "Faustian age" is used by some as a label to describe the epidemic of materialism that has erupted in the last couple of centuries or so. Faust, of course, made a contract with the Devil, which brought him worldly success and Mephistopheles was the go between. Some people see this story as an allegory for the souless socitey that grew up out of the Enlightenment and which promoted science rather than an understanding of spiritual values. The term, "Faustian age", then, is not a Great Age but a description for the last part of the Piscean Age and is just a term invented, like we would call the latter part of the 20th century the "jet age"!
As for Satan, he's trying to win the Grail, not by destroying humanity, but by achieving the aim of totally subjugating and controlling it. If he could achieve this, then he will have won the Grail because humanity is the vessel through which the greatest rays of the Grail shine on earth. As Satan no longer has any power of his own, as he was thrown out of Heaven, his only source of power comes through humanity, so it wouldn't be in his interest to totally destroy it, IMHO.