A 22 MPH top speed for a 500 Watt motor is pushing its limits as far as how much power it has so I would only recommend this reduction ratio if the scooter will only be used on flat and paved ground. If the scooter will be used to go up any grades or hills then I recommend a lower reduction ratio by using a 10 or 11 tooth sprocket on the motor.
Here is the gear ratio calculation with a 10 tooth motor sprocket.
And with an 11 tooth motor sprocket.
Please let us know if you have any questions.