Stanley M. Burgess dates the Gnostic movement from the first century CE and connects it, as did certain pre-Nicenes, with Simon Magus who is mentioned in Acts 8:
"The general label of 'Gnosticism' is used to describe a wide variety of religious systems and ideas that flourished from the first through the third centuries A.D., with some continuing well into the Middle Ages" (The Holy Spirit: Ancient Christian Traditions, page 35).
Burgess adds that Gnosticism was both syncretistic and contemplative since it simultaneously borrowed concepts from Jewish-Hellenic sources and advocated redemption through GNWSIS QEOU--a type of mystical knowledge that purportedly united the gnostic with the Divine One (i.e., God).
W.H.C. Frend ("The Rise of Christianity") further indicates that LXX Scriptures such as 1 Sam 2:3 evidently influenced the Gnostics to associate salvation with GNWSIS since Jehovah is there called "the God of knowledge." Frend actually places the "Acute Hellenization" of Christianity at 130-135 CE. And the Gnostics may have received additional impetus circa this time by interpreting the words of Isa 53 as prophetic of the deliverer who redeems humankind through GNWSIS. Of course, this type of exegesis probably skewed the original meaning of the passages in both Samuel and Isaiah.
The kind of Gnosticism which obtained in the first century must have been an incipient form at best. In fact, besides possibly manifesting themselves in Corinth and the so-called Johannine Community, there is evidence that Paul waged spiritual warfare against the Gnostics in Col 2:8. They are at least one of the enemies he may have wrestled with spiritually when he penned those famous words about the possible ill effects of worldly philosophy and tradition. At any rate, the Gnostics were anti-worldly, anti-corporeal and quite Platonically-oriented.
H.O.J. Brown's book on heresies also contains some enlightening information that pertains to this mysterious religious movement, whose ideas have been further clarified with the finding of the Nag Hammadi (Egypt) documents in the 1940s.