The oldest tree in the world is in California. It is 5,064 years old. Plants do not grow old the way mammals do. Many things could lead to the death of a tree. This includes a storm that knocks off a tree limb, exposure to disease, being struck by lightning or being blown over during a storm.
A tree may not die of old age, but after a long enough time, it may die of some other cause. When trees grow larger, they become more susceptible to stress due to a decrease in photosynthesis. Scientists have determined that it is the size of the tree that causes stress and wearing, not how old it is.
No living being dies of old age. When animals grow old and their cell division process deteriorates which creates problems in their bodily functions. Cell degeneration paves way for illnesses and diseases which ultimately becomes the cause of their death. For plants, age does not hinder their cell activity and they keep on growing. There exists trees which are more than 5000 years old. So age does not kill plants nor does it create any “cell” condition which causes their death.
But trees can die of other reasons such as parasitic attacks, insect manifestation, storms and harsh weather conditions.