While I'm concerned about the impacts of climate change and diseases, I am interested in the idea here that we can get to an average life expectancy of 100.
According to the actuarial tables Social Security uses [0] to estimate lifespan, a female born today has an average life expectancy of 81. 76 if you happen to be male.
Let's just focus on the female population since that number is better. What is the maximum age a given population could reach, considering all environmental factors are perfect? Is it much greater than 100? If not, won't it be very difficult to remove all of the environmental factors from consequence?
We would have to greatly reduce risks like heart disease and cancer, which collectively claim 1.2m lives a year in the US [1], which will take massive dietary changes. We'd also have to eliminate most accidental deaths, which are currently over 200k / year and include fun things like car accidents and opiate overdoses.
Assuming we make all of the changes, our world will be pretty different. People will eat a lot healthier, drive practically nowhere, and abstain from drinking and drug use. A tall order on a short timespan, but worth it if we can get there.
On the other hand, most of us like to eat what we want, drive where we want, have some drinks here and there, and receive pain meds when our risky behavior leads to an injury.
[0] https://www.ssa.gov/oact/STATS/table4c6.html
[1] https://www.cdc.gov/nchs/fastats/leading-causes-of-death.htm