I am 76 years old and my wife and I want to spend four or five days on Orkney. We are interested in the archeological sites and visiting churches in Kirkwall. Can we rent a car on the island, or should we plan to rent a car on the mainland and ferry to the islands?
You can fly in on LoganAir and there is a car rental agency at the Kirkwall airport. There is also an agency that lists a rental desk in the Kirkwall town centre.
Where are you planning to take the ferry from? I'm asking because there is a Northlink Ferry that sails Aberdeen to Kirkwall and another route that goes Scrabster to Stromness.
Pentland Ferries runs from Gills Bay to St Margaret's Hope.
If you arrive by ferry from Aberdeen you arrive at almost midnight, so won't need a car until the next day anyway. A bus runs from Hatston Port at Kirkwall the two miles into the town centre in connection with the arrival of the ferry (that ferry only runs 3 days a week).
If you arrive at Stromness by ferry there used to be a local rental company in town close to the port- Norman W Brass- however I don't believe that they survived the pandemic.
But a bus meets each ferry to take you into Kirkwall that evening, then rent next day. You reach Scrabster terminal by train to Thurso (then local taxi) or by direct ferry connecting bus from Inverness.
Likewise for the Pentland ferries route- buses serve Gills Bay Terminal from both Wick and Thurso railway stations and the other end of the Stromness bus route serves St Margaret's Hope terminal every hour to take you into Kirkwall over the Churchill Barriers and past the Italian Chapel.
Multiple companies (including the international ones) are at Kirkwall Airport- all are franchises run by various local companies.
All the ferry routes take foot passengers. If the days coincide Aberdeen is probably the easiest port to access, depending where else in Scotland you are starting from.
Some Auto Rentals may have a top 75 age limits. I would look online on the policy of agencies in Orkney. Maybe a tour to Kirkwall is available. Check to see if your own insurance covers international driving, so you won't have to pay extra insurance. It is probably not a good idea to take an auto on a long distance ferry unless you want to pay a lot extra. Better to walk on, or check flights as that may not be more expensive. Bon Voyage!