I am going to Amsterdam on the 4th of December and, although I have been driving for more than a year, I would like to know if i could hire a car being only 20 years old.
The driver must have held a full driving licence for at least one year, so you match this requirement.
To find out if there are suppliers that rent cars to young drivers, please follow these instructions: once you have done a search, click on the link "terms & conditions" displayed near the car photo of your choice. This will open a smaller window and if you click on "driver's age" you will see what age restrictions there may be and any associated fees. Try a few different car models / suppliers, as they do differ.