Cause 2 - Death Due To Cessation Of Kamma Forces
The kammic forces which conduce one's life will support that life from the embryonic stage towards until the day the forces cease to exits. There are also other kinds of kamma which enhance the principle life supporting kamma and when these kammic forces are exhausted, a person dies even though his life span has not expired. So if kammic forces cease at the age of 50, that person will die in spite of life span of 75. This is analogous to a flame dying out due to the wick burning out even though there still is oil in the lamp.