Any of you who have ever visited the church and graveyard at Clonmethan would certainly have seen the large beech tree (below). It was measured recently and has a circumference of 232 inches. Based on a calculator at tree-guide.com this puts it at 346 years old. This calculator has a tolerance of about 10% either way, giving a range of 312- 380 years old.
Assuming an age of 346, this tree was a seedling in 1674. Have a look here for some key facts of that year.