Not everyone is allowed to rent cars in Turkey. Your documents must be in order and you must be a certain minimum age. You will normally be asked for:
1. A valid passport (including, if required for your nationality, a valid visa) or, from European Union countries, an official Identity Card.
2. A valid credit card to pay for the estimated rental fees, plus a security deposit "hold" of perhaps US$1000/€900.
3. A valid driver's (driving) license. Normally you must have had your driver's license for at least a year before renting an inexpensive car, and perhaps two years for renting a more expensive model. If your driver's license is from a major country, and printed in the Latin alphabet, you do not normally need to have an International Driving Permit.
If your driver's license is in a writing system other than the Latin alphabet (Arabic, Chinese, Japanese, Korean, etc.) you may be required to have an International Driving Permit in addition to your driver's license. The IDP serves as a translation of your license.
4. A minimum age requirement. Normally you must be at least 21 years of age to rent, but some agencies may require you to be 23. For more expensive models, you may need to be at least 27 or 28 years of age.
Many agencies set an upper age limit of rentals at 70 to 75 years old.
5. All drivers wishing to drive the car must meet these requirements. You may have to pay an extra fee for an additional driver.