Being healthy is not the only factor for long lifespan, there are also accidental risks (disease, being eaten by a tiger, ...) mitigated by our modern way of life and access to advanced healthcare.

A Masai is probably healthier than a cliche westerner fueled processed carbs and sitting all day, but the latter will certainly live longer.

As for Japanese eating lots of rice, portion control ? I'd guess they get a large proportion of their calories from rice, but don't over-eat. I used to live in Thailand, Thais eat all the time, mostly carbs but small portions, and there are still fewer fat people than in the West.