If you are hiring a car in Ireland, you need to make sure that you can do so legally. Most car hire companies require you to be 8-12 years over the legal driving age in your home country. This doesn’t mean you have to have had your driver’s license for that long, but let’s say, if you are from USA or Canada, the legal driving age is 16 and the required minimum driving time is 9 years. This means you have to be at least 25 years old to hire a car in Ireland.
There are also restrictions on hiring a car if you are above 70 years of age. Each car hire company has their own regulations. Some might not hire you a car at all, others will require you to have an insurance with better coverage, others might require a note from your doctor that you are fit to drive.
Do your research and make sure you’re eligible to hire a car in Ireland.