Can an old guy rent a car?

Will I be able to rent a car?

Probably

Is there a surcharge for an old fella?

Maybe-- policy varies among the car rental companies

Your best bet is to check the various rental agencies and see what their policy is. Some allow it, some don’t, and some require medical documentation that you’re fit to drive. It may cost you a bit more, too.

In Greece, there is no legal age limit for renting a vehicle, however, individual rental companies may set their own policies, and in most cases, an additional fee applies to drivers over the age of 70. It is up to you to check the terms and conditions of the car rental companies in advance.

Aside from those at Athens Airport, the vast majority of car rental agencies in the city center are located along the same avenue: Syggrou-Fix. They are listed here (this is a partial list; you can adjust the map view):

https://maps.app.goo.gl/uZZoB3Zq8GpFqFRv5

Thank you folks!