"gnostic sects" were active and living before christ was even born?

Of course they were, which is why it is so dishonest that they subverted Christianity with later forgeries. They are different teachings entirely.

They can hardly subvert something that came after them

That doesn't even make sense. Of course they can. Christianity arose due to the life and miracles of Jesus. Gnostics seized on that for their own purposes with later Gnostic texts at odds with the four gospels.

"gnostic sects" were active and living before christ was even born?

Of course they were, which is why it is so dishonest that they subverted Christianity with later forgeries. They are different teachings entirely.

They can hardly subvert something that came after them

That doesn't even make sense. Of course something has to first exist before it can be subverted. Christianity arose due to the life and miracles of Jesus. Gnostics seized on that for their own purposes.