If your reading of the code is correct that would be 21, which is the Shift Spindle Angle Sensor.
Due to the low mileage and age I'd bet its either come unplugged or has water intrusion.
Under the passenger side rear floorboard (assuming it's a 5 seater) at the back of the engine is a blue connector running horizontally front to rear. Check to see if its plugged in, you could also try unplugging it and checking for water inside.
If that doesn't fix the issue, then the sensor could be at fault. In that case, turning the emergency valve in should force the unit into 2nd gear and get you back home.
Picture for reference:
View attachment 244171