Human lifespan has a natural limit – and we've already reached it

Check out Telomeres. Our limited number of them are what they're referring to.

Each human life has a unique expiration date SPC Britanny *Winnie* Balthaser. God knows exactly what that is but we don't. :-)
Some things we do can limited our life expectancy like smoking and drinking excessively, imbibing in illegal drug use, playing with guns, etc.
I went through Mitral-valve repair surgery at Walter Reed Army Medical Center in 2003 where doctors shut my heart down chemically and then restarted it electrically 12 hours or so late after most serious complications were resolved. My resting heart rate was over 100 beats per minute so I took heavy does of beta blockers to get it down. That helped for 10 years now my blood pressure medications have all been increased. The heart is an amazing organ which can take an amazing amount of abuse and still keep on beating to put the energizer bunny to shame :-)
A friend from church who recently went through tongue restoration surgery refused to stop smoking and now he has lung cancer in his early 60's.

You have an expiration date the day you are born, it just isn't printed anywhere on your body. We can effect our quality of life for whatever time our heredity gives us, by not abusing our bodies. That's all folks.