I don't know what the statistics are but the average age of the car fleet must be considerably older here in Sweden compared to Ireland. The same probably goes for many other countries in Europe I've certainly seen lots of older daily drivers on trips to France and Spain.
I'd hazard a guess that the very late introduction of the National car test in Ireland is a major factor. Also despite the historical high cost of cars in Ireland a large portion of the public maintain their cars with a bare minimum of servicing.
Their is no VRT on cars here so in the past they have been considerably cheaper to buy new than in Ireland but there isn't the same turnover of cars here people keep their cars for longer and generally keep them well serviced, also cars retain their value better here.
Another thing that I would say has a big influence is the car tax trap where in Ireland at a certain point in a car's life cycle a years road tax can cost more than the value of the car, that doesn't happen here as car tax is generally pretty cheap and as said before cars retain their value better.
The state of many Irish road surfaces over the last 40 years probably has a major influence as well.
I live just outside a town of approx. 20,000 population and there is an ocean of older cars in daily use. Not all Saabs and Volvos either, off the top of my head I regularly see at least 5 Mk 1 Audi 100's, there are 3 Mk 1 Granada Coupes unrestored and driven daily and a couple of Mk 2 Granada's, loads of Mk 2 Golfs and Jetta's and a few Mk 1 Golfs lots of other stuff as well, here is a photo of a '79 Opel Kadett I was behind on the way to the supermarket today, I see it regularly and he drives it on, I was hardly able to catch up to him to get a snap.
On a quick glance around the supermarket car park there was a Mk 2 Opel Ascona, a Mid 80's Honda Prelude and a slightly newer Accord along with the usual selection of Volvo 240's, 740's and 850's.