Hi Valerie,
It's a good question as, in the Republic of Ireland, it is necessary to
submit a medical report form if you are above the age of 75 years. Those ages 75 and older who are planning to rent a car in Ireland may also be asked to provide a letter from their doctor confirming that they are fit to drive.
However, I am not entirely sure if you, living in Northern Ireland with a UK driving licence, are required to have a doctor's letter confirming fitness to drive your own car. I would encourage you to
contact the Road Safety Authority in the Republic of Ireland as they will be best placed to answer you.
Regards,
Eoin