There is no proof that protein restriction actually extends lifespan in humans (or any primate). That's not a scientific fact. And hypothetically even if it did work to slightly extend lifespan, I see little point in just being alive if I'm too weak and frail to do the activities I enjoy.

> (2) protein restricted diet slows down aging.

Protein/calorie restricted diet is observed to slow down aging in rats in laboratory conditions, i.e. which make no other changes to their presumably sedentary lifestyles.

Protein restriction in humans is only recommended if you have some chronic kidney disease. If I remember right, most people don't consume enough protein to need to restrict in this case either.