1 - We should study health in order to understand the human body better as well as to understand what not to do in order to stay as healthy as possible. We also study health in order to be able to identify other signs of diseases and such and learn how to treat injuries on our own.
2 - Emotional health focuses more on actual feelings such as empathy, anger, etc. Mental health focuses on the mental state of a human and mental diseases and such.
3 - Life expectancy has increased due to the fact that society has begun to understand health better and how to survive better. On top of that, technologies have increased throughout the years to help with medicine for diseases.
4 - Everything influences your health. Genetics, the environment, other people, genetically modified things.
5 - This can be varied based on the answer-er as everyone has a different heredity and heritage.
Hope this helps!