The second and third sentence of this do not support the first.

It's true that a lot of people (all over the world) make lifestyle choices which probably shorten their lifespan. Although I think you're understating the simplicity of losing significant weight / quitting smoking / drinking less, all of which are things which are notoriously difficult.

It does not follow that those people wouldn't notice an additional five years of lifespan. Of course they would, it's five years!

If someone was selling pills you could take twice a day to add five years of lifespan, the number of people who would take them is broadly limited by the number who could afford to.

It is also important to note 'where' you are adding the five years. An additional five years of infirmity at the end of life? Pass. An additional five years of relatively healthy mid-60s? Sign me up.

Extending lifespan is less useful than extending the healthy/active part of the lifespan. Like reading the fine print on the side of the packaging or the bottom of the contract, you need to pay attention to the details. This is why lifestyle changes tend to be more important than pills which treat conditions that used to kill our parents or grandparents, the former usually increase the odds you will still be walking around and taking care of yourself in your late 80s while the latter might just mean that you add five years to the amount of time that some nursing home will drain your estate while you are bed-ridden in some warehouse for the elderly.

I still disagree. I spent a lot of time in nursing homes when I was a teenager and am quite confident that adding five years of elderly life would not only not be noticed by many people who are just whiling away their later years, a lot of them wouldn’t even want it. You’re assuming that a magic pill adding five years of longevity would either distribute those years equally or primarily extend youthful years, but it’s not at all clear that that’s the case.