Sheep can live from twelve to fourteen years.
They are not happy living without other sheep - you need at least two.
You can check veterinary recommendations for minimum spacing requirements. In my experience, sheep are happier with more space. A small pen will bore them. It's also healthier for them to have access to fresh grass and pasture forage during the growing season. They won't enjoy a diet of only hay all year long - it's the difference between what will keep them alive and what they will really thrive on.
I stock my fields at five ewes per acre generally, but I also do some rotations. You could probably keep two sheep on 1/2 an acre depending on what types of grass you have. At some point, though, you will have to move them out of that area and let it rest or even reseed it.