Question: Is the lifespan of every person is predetermined from the day one is born?
Answer: With any set of karmic conditions at any one point in time, it is as if one’s lifespan is fixed at that point in time. However, as we create fresh karma while living, this new karma interacts with the karma already present, and presents new possibilities. As such, even though lifespan seems predetermined at times, it is not. A classic true story that exemplifies how our life is dynamic can be found in ‘The Four Lessons of Liaofan’ at http://buddhanet.net/liaofans.htm
The Old & Young Monks Who Killed Ants