Of course you are correct, but it still needs to be considered. Ultimately we are slowly fighting against everything that eventually kills us. we take a reduction in infant mortality as "matter of fact" but let me tell you, my second son was born 3 weeks ago and my wife and I did not get to the hospital in time and I had to deliver him myself on our bedroom floor. Miraculously everything went well and the ambulance arrived seconds later to take both him and my wife to the hospital, but it was such a dangerous situation. After that I will never take infant mortality for granted again.

With regards to your statement about people living almost as long as today, I disagree with. Yes 40 was never considered "old age" (as far as I am aware) but 50 and 60 definitely was. Living to 60, 300 years ago, would be like living to 100 today, very unusual and only perfect health, diet and environment would get you there. Now my dad is in his 60's working at a comfortable rate, and getting plenty of exercise and apart from type 1diabetes, has no major health concerns.

People are living longer, its just a fact, yes infant mortality skewes the data, but if you remove infant mortality from the data, I believe we have atleast doubled life expectancy from when modern humans first evolved.