as far as i know he would be entitled to the state pension. and you never know those farmers can be fairly savy, especially if he had an accountant do his returns all these years.
He can apply for the means-tested state pension (old age). If he is still farming, his income will be assessed but some will be disregarded. Every individual case is different. Check out www.welfare.ie for details as to how income is assessed. I think there is also some sort of retirement scheme for farmers who transfer land to others.