Medicine hasn't even attempted to extend human lifespan. To date it has only adressed causes of premature death. These conclusions have this baked-in as a (quite probably unconscious) assumption. Medicine needs to grow beyond this short-sightedness.
Also, medicine is only concerned about bringing people with problems back to the "average normal" health state. What if I want to improve on the average?
CRISPR allows for the in place editing of your genome, which is going to be necessary to extend your life significantly or make you an above average human.
Working out regularly would certainly make your "health state" better than average.
This will just turn into a silly argument over semantics. It's not as if a natural death is just suddenly passing from old age. You succumb to some kind of disease that destroys a critical part of your body. Modern medicine does a lot when it comes to preventing and curing diseases, so I'm not sure where your argument that medicine hasn't attempted to extend our lives comes from.
The effects of aging aren't recognized as a disease. I'm all for changing that and treating aging as a disease. That's the distinction I'm making. Barring diseases and injuries, the human lifespan hasn't been extended. The average lifespan has been extended because we can treat diseases and injuries -- that is wonderful. The lifespan of a healthy person -- how long a disease- and injury-free person can live -- hasn't changed, and that's medicine's blind spot I was talking about.