Can you believe that there are living organisms on the Earth that are over 5,000 years old?

I find it practically unbelievable, but a man cut a tree down to count the rings, only to find that he had killed an organism 4,900 years old! They have since found a living tree that’s believed to be over 5,000 year old.

Is there perhaps some anomaly that that could cause a tree to produce more than one ring per year?

It was mentioned that the oldest animal is (I believe) an oyster, at about 500 years old.