Effect of Input Frequency on Output of Class A amplifier
At the moment, you're directly applying a "hard" voltage to the base of Q1. That is unrealistic and can never be done in a real circuit. Try adding a resistor of 1 kohm in series with C2.

Normally in this circuit the collector-base capacitance of the transistor is the main factor that limits the bandwidth. This capacitor is often referred to as a Miller capacitance because the value of the actual collector-base capacitance is enlarged by the gain of the circuit, this is called the Miller effect.

When you apply a "hard" voltage at the base then this Miller effect is cancelled out so you will see an unrealistic high bandwidth value.

Other factors that influence the bandwidth are load capacitance, which is zero in your circuit which is also unrealistic. When you build this circuit and measure at the output with an oscilloscope probe you add a few pF of capacitance since the oscilloscope's probe has some input capacitance.