All drivers need to be at least 21 with a driver’s license held for at least 1 year. Some car categories require renters to be 25, and a young driver surcharge applies to those under 23.
All renters need a valid driver’s license held for at least 1 year, plus an ID or passport. Those with a driver’s license using a non-Roman alphabet like Arabic will also need an international driving permit.
Generally, one-way rentals are allowed between SIXT stations in Greece. You will need permission from the branch you want to rent from.