> German driving licence would be good to rent a car for 1 month or do
> we need an international driving licence?

You can usually rent a car and drive with a valid driver's license from your home country in USA. An international license may be helpful in convincing the car rental agent that you really have a valid license when they cannot recognize or understand your license. 

From the official  [USA.GOV](https://www.usa.gov/visitors-driving#item-37267):

"Short-Term Visitors

If you intend on getting an IDP, you must do so in advance of your travel:

 - The United States does not issue IDPs to foreign visitors. To get an
   IDP, contact the motor vehicle department of the country that issued
   your driver's license.
 - If you want to rent a car, **you may need both your license and an IDP**.
   Find out the rental company's policies and other requirements in
   advance."

Also From [Florida HIghway Safety And Motor Vehicles](https://www.flhsmv.gov/driver-licenses-id-cards/visiting-florida-faqs/):

**Visiting from another country?**

Visitors to Florida who wish to drive while here are required to have in their immediate possession a **valid driver license issued in his or her name from their country of residence.**

If renting a car while visiting Florida, we suggest you check with the rental car company prior to your visit to see what they require. However, it’s our understanding that rental car companies have not changed their procedures or requirements for having a valid driver license from any state, U.S. territory or foreign country.

Similarly when we look at rental car company requirements because it is recommendation from official USA.GOV website we get the following result:

1 [Enterprise](https://enterprise.custhelp.com/app/answers/detail/a_id/8491/~/what-are-your-driver-license-requirement-for-renting-in-the-us-and-canada%3F#/) :

Customers traveling to the United States and Canada from another country must present the following:

 - Their home country driver's license, and
 - If the home country license is in a language other than English (or
   French, for rentals in Canada) and the letters are English (i.e.
   **German,** Spanish, etc.) an International Driver's Permit is
   recommended, but not required, for translation purposes in addition
   to the home country license.
 - If the home country license is in a language other than English and
   the letters are not English (i.e.alphabet is not an extended
   Latin-based alphabet like German or Spanish but is Russian, Japanese,
   Arabic, etc.) an International Driver's Permit is required.

Also when we look at another rental car company [Hertz](https://www.hertz.com/rentacar/reservation/reviewmodifycancel/templates/rentalTerms.jsp?KEYWORD=LICENSE&EOAG=LAX), we also get the same recommendation:

" If the driver's license is in a language other than English, and the rental is in the United States, an International Driver's Permit is recommended.  In all cases, a valid driver's license issued from your home country must be provided, whether or not you possess an International Driver's Permit.  You will not be allowed to rent a Hertz vehicle with only an International Driver's Permit."

Therefore, your German drivers licence would be acceptable licence in USA, however you will also need an international driver permit (IDP) because it is recommended by both USA.GOV and by car rental companies. Also you need a valid credit card in order to rent a car in USA.

> Any age restrictions to rent a car in USA?

No. Provided you have a current valid driving license. There is additional surcharge for younger drivers under the age of 25, for both of you with the age of 60 and 55 there would be no problem for renting a car in Florida and USA.

Source: [US Car Hire](https://www.uscarhire.com/faq-restrictions.aspx)