The United States has about six violent deaths per 100,000 residents and none of the 16 other countries included in the review came anywhere close to that ratio.
Let's say that the average age of death of those 6 people is 20 and their life expectancy would have been 80 years. So you lose 6*60=360 years of life expectancy per 100,000 people or an average of 1.3 days of life expectancy. I expect that potato chips have a greater effect.
I think your math is correct but I'm betting it only applies for one year. Don't you have to multiply by 80 or so to get the effect on you?
I'm assuming that the 6 per 100,000 is per year even though the article doesn't say so.
Even so, potato chips are probably a bigger problem.