Welcome to the community!
First of all, it's great to hear that you are planning a trip to come and see us. Ireland is a wonderful place for a driving tour with so much beautiful coastline to explore.
I have included a link to Traveling in Ireland
, which gives some good general information about driving in Ireland.
For your specific question, I have a link to our web page containing information about Renting a car in Ireland
. It is still possible to rent a car, as Ireland has no upper limit to driving. However, rental companies may have additional requirements for someone over the age of 75. I would suggest contacting various companies in advance to make sure you meet these requirements.
We have several posts regarding car rental on our forum, take a look at these to see if they offer additional information.Car RentalCar Rental in Ireland
I will also leave it open for other community members to add their own experiences and information.