Why does a frisbee stay in the air so long?

It doesn't always. I tall depend son how the thrower throws it.

it stays up because of how fast it pushes air as long as it gose super fast it stays up

Like the wing of an aircraft, the downward curve of the outside edge of a frisbee makes the distance the air has to travel over the top greater than the distance across the bottom. That difference creates lift as long as the forward speed is great enough to keep the air moving over and under it. When the energy of the toss runs out and it loses the forward speed, it comes down like an aircraft when the airspeed has fallen below the minimums and it stalls.

To demonstrate the difference the lift makes, try throwing the frisbee upside down.