Moroni 10
100 years passed from the time Mormon was 10 and the time that Moroni died. Even if Mormon was 40 years old before Moroni was born that would mean that Moroni lived to be at least 70. We also know that Moroni was a commander among the Nephite armies at the last battle of Cumorah almost 40 years before he sealed up the plates. Also, we know that his first writings were 15 years after that last battle, it is possible that Mormon lived for a good portion of that time.