Yes, it is generally possible to book a rental car from the age of 18. However, you cannot book every car and often have to expect additional charges.
If you enter your age immediately before searching on billiger-mietwagen.de, the results will only show offers that you can rent according to your age. Any additional costs resulting from age are already included.
In addition to the rental company, the vehicle category or the place of rental often determine the minimum age for the rental car. The vast majority of providers set lower age limits for small and mid-range cars such as Golfs compared to luxury cars. Young drivers increase their chances of renting a car under 21 by opting for a small car. With Avis/Budget, for example, you can get this kind of rental car from the age of 19.
The golden rule for driving licence ownership: The minimum is always one year. Driving licences less than one year old are not accepted on site.