Hi Charles,
I'm sorry to hear you're experiencing this. It's great that you've been coming to Ireland for so many years, with your friends and family.
From what I understand, you can hire a car when you're over the age of 75, but some rental companies can ask you to meet certain requirements. This could be a letter from a doctor or something similar. I truly don't believe these conditions have anything to do with bad experiences! They are mainly related to insurance. Rental agencies usually mention their requirements in their terms and conditions, but I'm sure they'd be happy to provide more information if you give them a call or send them an email.
You're not the first person to ask this question on here. I've found two related threads, and the answers to those might be useful to you as well. You can check out these threads on
Car rental and
Car hire in Ireland.
I hope that you find a rental agency that can help you out. There might be others on here who can give more tips or even recommend a car rental agency.
Have a lovely day,
Noortje